Driving apparatus for vehicle

ABSTRACT

A vehicle driving apparatus includes: an engine; a fluid transmission device; first and second rotary electric machines; an output shaft for receiving a power transmitted through a first power transmission path and outputting the power to one of a pair of front wheels and a pair of rear wheels; and a control device for controlling an engine operation point by adjusting an electrical path amount between the first and second rotary electric machines. The second rotary electric machine outputs the power to the other of the pair of front wheels and the pair of rear wheels, through a second power transmission path. The control device obtains a target electrical path amount enabling the engine operation point to become a target operation point, and causes a speed change device provided in the second power transmission path to establish a gear ratio enabling the target electrical path amount to be attainable.

This application claims priority from Japanese Patent Application No. 2021-100532 filed on Jun. 16, 2021, the disclosure of which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a driving apparatus for a vehicle, wherein the driving apparatus is capable of controlling an engine operation point by adjusting an electrical path amount between a first rotary electric machine and a second rotary electric machine.

BACKGROUND OF THE INVENTION

There is proposed a driving apparatus for a vehicle, comprising: (a) an engine; (b) a fluid transmission device including an input-side rotary element configured to receive a power from the engine and an output-side rotary element configured to output the power received by the input-side rotary element; (c) a first rotary electric machine directly or indirectly connected to the input-side rotary element; (d) a first output shaft which is configured to receive the power outputted by the output-side rotary element and transmitted through a first power transmission path and which is configured to output the power to one of the pair of front wheels and the pair of rear wheels; (e) a second rotary electric machine; and (f) a control device configured to control an operation point of the engine by adjusting an electrical path amount that is an amount of an electric power in an electrical path through which the electric power is to be transferred between the first and second rotary electric machines. An example of such a driving apparatus is disclosed in Patent Document 1. In this Patent Document 1, it is described that a fuel economy of the engine is improved by bringing the operation point of the engine close to a fuel-economy optimum line by adjusting the electrical path amount.

PRIOR ART DOCUMENTS

-   [Patent Document 1] Japanese Patent No. 5700124 -   [Patent Document 2] Japanese Patent Application Publication No.     2013-159141

SUMMARY OF THE INVENTION

By the way, in the driving apparatus constructed as described, an output characteristic of the second rotary electric machine is dependent on a rotational speed and a torque of the second rotary electric machine, and the attainable electrical path amount is limited by the output characteristic of the second rotary electric machine, so that there is a room for improvement in the fuel economy of the engine.

The present invention was made in view of the background art described above. It is therefore an object of the present invention to provide a driving apparatus for a vehicle, which is configured to control an operation point of an engine by adjusting an electrical path amount between first and second rotary electric machines, and which is capable of further improving a fuel economy of the engine. This object is achieved according to the following aspects of the present invention.

According to a first aspect of the invention, there is provided a driving apparatus for a vehicle, the driving apparatus comprising: comprising: (a) an engine; (b) a fluid transmission device including (b-1) an input-side rotary element configured to receive a power from the engine and (b-2) an output-side rotary element configured to output the power received by the input-side rotary element; (c) a first rotary electric machine connected to the input-side rotary element; (d) a first output shaft which is configured to receive the power outputted by the output-side rotary element and transmitted through a first power transmission path and which is configured to output the power to one of the pair of front wheels and the pair of rear wheels; (e) a second rotary electric machine; and (f) a control device configured to control an operation point of the engine by adjusting an electrical path amount that is an amount of an electric power in an electrical path through which the electric power is to be transferred between the first and second rotary electric machines, wherein the second rotary electric machine is configured to output the power to the first output shaft or the other of the pair of front wheels and the pair of rear wheels, through a second power transmission path that is other than the first power transmission path, wherein the second power transmission path is provided with a speed change device that is configured to change a speed of rotation of the second rotary electric machine in accordance with a currently established one of gear ratios that is established in the speed change device and to output the rotation whose speed has been changed, wherein the control device is configured to obtain a target electrical path amount as a target amount of the electrical path amount that enables the operation point of the engine to become a target operation point, and to control the speed change device based on the obtained target electrical path amount so as to establish one of the gear ratios that enables the obtained target electrical path amount to be attainable; and wherein the control device is configured to adjust the electrical path amount to the obtained target electrical path amount, and to control the operation point of the engine.

According to a second aspect of the invention, in the driving apparatus according to the first aspect of the invention, when at least two of the gear ratios enable the obtained target electrical path amount to be attainable, the control device is configured to cause the speed change device to establish one of the at least two of the gear ratios that maximizes an efficiency of the second rotary electric machine.

According to a third aspect of the invention, in the driving apparatus according to the first or second aspect of the invention, in an event that the speed change device cannot execute a shifting action for switching a currently established one of the gear ratios to another one of the gear ratios, the control device is configured to limit the electrical path amount depending on the currently established one of the gear ratios.

According to a fourth aspect of the invention, in the driving apparatus according to any one of the first through third aspects of the invention, there is provided a second output shaft configured to output the power to the other of the pair of front wheels and the pair of rear wheels, wherein the speed change device includes: a differential device including a first rotary element connected to the second rotary electric machine, a second rotary element connected to one of the first and second output shafts and a third rotary element connected to the other of the first and second output shafts, the differential device constituting a torque distribution device that is configured to distribute a part of a torque inputted to the first output shaft, to the second output shaft; a first engagement device configured to connect and disconnect between two of the first, second and third rotary elements; and a second engagement device configured to connect and disconnect between the third rotary element and a non-rotary member.

In the driving apparatus according to the first aspect of the invention, the control device is configured to obtain the target electrical path amount that enables the operation point of the engine to become the target operation point, and to control the speed change device based on the obtained target electrical path amount so as to establish one of the gear ratios that enables the obtained target electrical path amount to be attainable, and the control device is configured to adjust the electrical path amount to the obtained target electrical path amount, and to control the operation point of the engine. Thus, it is possible to restrain the electrical path amount from being limited by the output characteristic of the second rotary electric machine. Consequently, the engine can be operated at the operation point that improves the fuel economy of the engine.

In the driving apparatus according to the second aspect of the invention, when at least two of the gear ratios enable the obtained target electrical path amount to be attainable, the control device is configured to cause the speed change device to establish one of the at least two of the gear ratios that maximizes the efficiency of the second rotary electric machine. It is therefore possible to improve an efficiency of the electrical path.

In the driving apparatus according to the third aspect of the invention, in the event that the speed change device cannot execute the shifting action for switching the currently established one of the gear ratios to another one of the gear ratios, the control device is configured to limit the electrical path amount depending on the currently established one of the gear ratios. It is therefore possible to limit the electrical path amount to an appropriate amount.

In the driving apparatus according to the fourth aspect of the invention, the speed change device is constructed to include the differential device constituting the torque distribution device, so that it is possible to suppress increase the number of components required for the speed change device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing a construction of a driving apparatus for a vehicle to which the present invention is applied, for explaining major control functions and control portions provided for performing various control operations in the vehicle driving apparatus;

FIG. 2 is a view schematically showing a construction of a hybrid transmission shown in FIG. 1 ;

FIG. 3 is a table indicating a relationship between each gear position of an automatic transmission shown in FIG. 2 and a combination of engagement devices that are to be placed in engaged states to establish the each gear position;

FIG. 4 is a view schematically showing a construction of a transfer shown in FIG. 1 ;

FIG. 5 is a collinear chart indicating a relationship among rotational speeds of rotary elements of the transfer of FIG. 4 ;

FIG. 6 is a table indicating a relationship between each mode established in the transfer of FIG. 4 and controlled states of respective engagement devices in the transfer of FIG. 4 ;

FIG. 7 is a view showing, by way of examples, an AT-gear-position shifting map used for controlling gear shifting in the automatic transmission, a driving-mode switching map used for switching a driving mode, and a relationship between the shifting map and the driving-mode switching map;

FIG. 8 is a view for explaining that an engine operation point can be changed as in a continuously-variable transmission, in the vehicle driving apparatus;

FIG. 9 is a view showing a motor characteristic of a TF rotary electric machine;

FIG. 10 is a flow chart showing a main part of a control routine that is to be executed by an electronic control device, for improving a fuel economy of an engine, by appropriately controlling an operation point of the engine by selecting a suitable gear ratio of a differential device during running of the vehicle;

FIG. 11 is a flow chart showing a main part of a control routine that is to be executed by an electronic control device according to another embodiment of the present invention, for improving the fuel economy of the engine, by appropriately setting an electrical path amount in a state in which a gear position of the differential device is fixed;

FIG. 12 is a view schematically showing a construction of a transfer in another embodiment of the present invention;

FIG. 13 is a collinear chart indicating a relationship among rotational speeds of rotary elements of the transfer of FIG. 12 ; and

FIG. 14 is a table indicating a relationship between each mode established in the transfer of FIG. 12 and controlled states of respective engagement devices in the transfer of FIG. 12 .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. It is noted that the figures of the drawings are simplified or deformed as needed and portions are not necessarily precisely depicted in terms of dimension ratio, shape, etc.

First Embodiment

FIG. 1 is a view schematically showing a construction of a vehicle driving apparatus 10 to which the present invention is applied, for explaining major control functions and control portions provided for performing various control operations in the vehicle driving apparatus 10. As shown in FIG. 1 , the vehicle driving apparatus 10 includes power sources in the form of an engine 12 (that is represented by “ENG” in FIG. 1 ), a TM rotary electric machine MGM and a TF rotary electric machine MGF. Thus, a vehicle 8, in which the vehicle driving apparatus 10 is to be provided, is a hybrid electric vehicle having right and left front wheels (a pair of front wheels) 14 and right and left rear wheels (a pair of rear wheels) 16. The vehicle driving apparatus 10 includes a power transmission device 18 configured to transmit powers of the power sources such as the engine 12, to the front and rear wheels 14, 16. The engine 12, TM rotary electric machine MGM and TF rotary electric machine MGF will be simply referred to as “power sources PU” unless they are to be distinguished from one another. The power sources PU include a first power source PU1 constituted by each of the engine 12 and the TM rotary electric machine MGM that output the powers to be transmitted to a torque converter 48 and an automatic transmission 50 (that will be described below), and a second power source PU2 which is constituted by the TF rotary electric machine MGF provided in a transfer 28 (that will be described below) and which is to be used as the power source in addition to or in place of the first power source PU1. It is noted that the rear wheels 16 correspond to “one of the pair of front wheels and the pair of rear wheels” recited in the appended claims, that the front wheels 14 corresponds “the other of the pair of front wheels and the pair of rear wheels” recited in the appended claims, that the TM rotary electric machine MGM corresponds to “first rotary electric machine” recited in the appended claims, and that the TF rotary electric machine MGF corresponds to “second rotary electric machine” recited in the appended claims.

The vehicle 8 is an all-wheel drive vehicle capable of distributing a part of a torque, which is transmitted by the vehicle driving apparatus 10 to the rear wheels 16, to the front wheels 14. The vehicle driving apparatus 10 is capable of performing a rear-wheel drive by which the torque is transmitted only to the rear wheels 16 (that correspond to “one of the pair of front wheels and the pair of rear wheels” recited in the appended claims) and also a front-wheel drive by which the torque is transmitted only to the front wheels 14 (that correspond to “the other of the pair of front wheels and the pair of rear wheels” recited in the appended claims). The vehicle 8 is also a four-wheel drive vehicle having four wheels consisting of the pair of front wheels 14 and the pair of rear wheels 16. In the description of the present embodiment, an all-wheel drive (=AWD) is synonymous with a four-wheel drive (=4WD). Each of the rear-wheel drive and the front-wheel drive is a two-wheel drive (=2WD). The front wheels 14 and rear wheels 16 will be simply referred to as “drive wheels” unless they are to be distinguished from one another.

The engine 12 is a known internal combustion engine such as gasoline engine and diesel engine. The driving apparatus 10 is provided with an engine control device 20 that includes a throttle actuator, a fuel injection device and an ignition device. With the engine control device 20 being controlled by an electronic control device 130 that is described below, an engine torque Te, which is an output torque of the engine 12, is controlled.

Each of the TM rotary electric machine MGM and the TF rotary electric machine MGF is a rotary electric machine having a function serving as a motor for generating a mechanical power from an electric power and also a function serving a generator for generating an electric power from a mechanical power. That is, each of the TM rotary electric machine MGM and the TF rotary electric machine MGF is a so-called “motor generator”. Each of the TM rotary electric machine MGM and the TF rotary electric machine MGF is connected to a battery 24 via an inverter 22, wherein the battery 24 and the inverter 22 are both provided in the vehicle driving apparatus 10. With the inverter 22 being controlled by the electronic control device 130 that is described below, an MGM torque Tmgm as an output torque of the TM rotary electric machine MGM and an MGF torque Tmgf as an output torque of the TF rotary electric machine MGF are controlled. The battery 24 is a power storage device to and from which the electric power is to be supplied from and to each of the TM rotary electric machine MGM and the TF rotary electric machine MGF. The above-described electric power corresponds to an electric energy, unless otherwise specified. Similarly, the above-described power corresponds to a drive power, a torque and a force, unless otherwise specified.

The power transmission device 18 includes a hybrid transmission 26 (see “HEV T/M” in FIG. 1 ), the transfer 28 (see “T/F” in FIG. 1 ), a front propeller shaft 30, a rear propeller shaft 32, a front differential device 34 (see “FDiff” in FIG. 1 ), a rear differential device 36 (see “RDiff” in FIG. 1 ), right and left front drive shafts 38 and right and left rear drive shafts 40. In the power transmission device 18, the power is transmitted from the first power source PU1 to the transfer 28 via the hybrid transmission 26, and then is transmitted from the transfer 28 to the rear wheels 16 sequentially via the rear propeller shaft 32, rear differential device 36 and rear drive shafts 40, for example. Further, in the power transmission device 18, when a part of the power transmitted from the first power source PU1 to the transfer 28 is to be distributed to the front wheels 14, the part of the power is transmitted to the front wheels 14 sequentially via the front propeller shaft 30, front differential device 34 and front drive shafts 38, for example.

The hybrid transmission 26 includes a non-rotary member (i.e., fixed member) in the form of a transmission case 42. The transfer 28 includes a non-rotary member (i.e., fixed member) in the form of a transfer case 44 that is connected to the transmission case 42. The TM rotary electric machine MGM is disposed inside the transmission case 42. The TF rotary electric machine MGF is disposed inside the transfer case 44.

FIG. 2 is a view schematically showing a construction of the hybrid transmission 26. As shown in FIG. 2 , the hybrid transmission 26 includes a connection shaft 46, the torque converter 48 and the automatic transmission 50 which are provided inside the transmission case 42 and which are disposed on a common axis in the form of a rotation axis CS1. Each of the torque converter 48 and the automatic transmission 50 is constructed substantially symmetrically about the rotation axis CL1, so that its lower half (that is located on a lower side of the rotation axis CL1) is not shown in FIG. 2 . The rotation axis CL1 corresponds to an axis of a crankshaft of the engine 12, an axis of the connection shaft 46 connected to the crankshaft, an axis of a transmission input shaft 52 that is an input rotary member of the automatic transmission 50 and an axis of a transmission output shaft 54 that is an output rotary member of the automatic transmission 50.

The connection shaft 46 is a rotary shaft connecting between the engine 12 and the torque converter 48. The TM rotary electric machine MGM is connected to the connection shaft 46 in a power transmittable manner. The torque converter 48 is a fluid transmission device including a pump impeller 48 a connected to the connection shaft 46, and a turbine impeller 48 b connected to the transmission input shaft 52. The pump impeller 48 a is connected to the TM rotary electric machine MGM via the connection shaft 46. The pump impeller 48 a is an input member of the torque converter 48, and is an input-side rotary element of the torque converter 48 to which the engine 12 is connected in a power transmittable manner. The turbine impeller 48 b is an output member of the torque converter 48, and is an output-side rotary element of the torque converter 48 to which the drive wheels are connected in a power transmittable manner. TM rotary electric machine MGM is connected to the connection shaft 46 in a power transmittable manner, namely, is connected to the pump impeller 48 a in a power transmittable manner. The connection shaft 46 is also an input rotary member of the torque converter 48. The transmission input shaft 52 is also an output rotary member of the torque converter 48 which is provided integrally with a turbine shaft that is to be driven and rotated by the turbine impeller 48 b. The torque converter 48 is a fluid transmission device configured to transmit the power of the first power source PU1 to the transmission input shaft 52 through fluid. The torque converter 48 includes a lockup clutch LU configured to connect between the pump impeller 48 a and the turbine impeller 48 b.

The automatic transmission 50 is disposed in a power transmission path between the torque converter 48 and the transfer 28. The transmission output shaft 54 is connected to the transfer 28. The automatic transmission 50 is a mechanical transmission device configured to transmit the power of the first power source PU1 to the transfer 28. Thus, each of the torque converter 48 and the automatic transmission 50 is configured to transmit the power of the first power source PU1 to the transfer 28.

The automatic transmission 50 is a known automatic transmission of planetary gear type that includes, for example, a plurality of planetary gear devices in the form of first and second planetary gear devices 56, 58, and a plurality of engagement devices in the form of a one-way clutch F1, clutches C1, C2 and brakes B1, B2. Hereinafter, the clutches C1, C2 and the brakes B1, B2 will be simply referred to as “engagement devices CB” unless they are to be particularly distinguished from one another.

Each of the engagement devices CB is a known hydraulically-operated frictional engagement device in the form of a multiple-disc type or a single-disc type clutch or brake that is to be pressed by a hydraulic actuator, or a band brake that is to be tightened by a hydraulic actuator. Each of the engagement devices CB is configured to receive a CB hydraulic pressure PRcb that is a regulated hydraulic pressure supplied from a hydraulic control circuit or unit 60 (see FIG. 1 ) provided in the vehicle driving apparatus 10, whereby a CB torque Tcb, i.e., torque capacity of the engagement device CB is changed and its controlled or operation state is switched between an engaged state and a released state, for example. The hydraulic control unit 60 is to be controlled by the electronic control device 130 that is described below.

In the automatic transmission 50, rotary elements of the first and second planetary gear devices 56, 58 are to be connected to each other directly or indirectly via the engagement devices CB or the one-way clutch F1, or are to be connected directly or indirectly to the transmission input shaft 52, the transmission case 42 or the transmission output shaft 54. The rotary elements of the first planetary gear device 56 are a sun gear S1, a carrier CA1 and a ring gear R1. The rotary elements of the second planetary gear device 58 are a sun gear S2, a carrier CA2 and a ring gear R2.

The automatic transmission 50 is a step-variable automatic transmission configured to establish a selected one of a plurality of gear positions, with a corresponding one or ones of the engagement devices CB being engaged, wherein the gear positions are different from each other in gear ratio (speed ratios) γat (=AT input rotational speed Ni/AT output rotational speed No). The automatic transmission 50 is configured to switch from one of the gear positions to another one of the gear positions, namely, to establish one of the gear positions which is selected, by the electronic control device 130, depending on, for example, an accelerating operation made by a vehicle driver (operator) and a running speed V of the vehicle 8. In the description of the present embodiment, the gear positions that are to be established in the automatic transmission 50 will be referred to as “AT gear positions”. The AT input rotational speed Ni is a rotational speed of the transmission input shaft 52, and is an input rotational speed of the automatic transmission 50. The AT input rotational speed Ni is equal to a turbine rotational speed Nt that is a rotational speed of the turbine shaft that is to be driven and rotated by the turbine impeller 48 b. The AT output rotational speed No is a rotational speed of the transmission output shaft 54, and is an output rotational speed of the automatic transmission 50.

As shown in a table of FIG. 3 , the automatic transmission 50 is configured to establish a selected one of the plurality of AT gear positions including four forward gear positions. Among the four forward gear positions, an AT1-speed gear position (represented by “1st” in the table of FIG. 3 ) provides the highest gear ratio γat, and an AT4-speed gear position (represented by “4th” in the table of FIG. 3 ) provides the lowest gear ratio γat and enables the vehicle 8 to run at a higher running speed V than the other gear positions. The table of FIG. 3 indicates a relationship between each of the AT gear positions and a combination of the engagement devices CB that are to be placed in engaged states to establish the each of the AT gear positions. In the table, “◯” indicates that the corresponding engagement device CB is placed in its engaged state, “Δ” indicates that the corresponding engagement device CB is placed in its engaged state during application of an engine brake to the vehicle 8 or during a coasting shift-down action of the automatic transmission 50, and blank indicates that the corresponding engagement device CB is placed in its released (disengaged) state. With any one of the four forward gear positions being established in the automatic transmission 50, the automatic transmission 50 is placed in a power transmittable state in which the power is transmittable through the automatic transmission 50. In a neutral state (represented by “N” in the table of FIG. 3 ) of the automatic transmission 50 which is established, for example, with all of the engagement devices CB being placed in the released states, the automatic transmission 50 is placed in a power untransmittable state in which the power is not transmittable through the automatic transmission 50, namely, a power transmission through the automatic transmission 50 is cut off. When the vehicle 8 is to run in a reverse direction, the automatic transmission 50 is placed in the neutral state (see “Rev” in the table of FIG. 3 ), with the power being outputted by the TF rotary electric machine MGF, for example.

FIG. 4 is a view schematically showing a construction of the transfer 28. As shown in FIG. 4 , the transfer 28 includes a TF input shaft 62, a differential device 64, a TF clutch CF1, a TF brake BF1, a first output shaft 66, an intermediate shaft 68, first and second dog clutches D1, D2 and a drive gear 70, which are provided inside the transfer case 44 and which are disposed on the common rotation axis CL1. Each of the differential device 64, TF clutch CF1, TF brake BF1, intermediate shaft 68, first and second dog clutches D1, D2 and drive gear 70 is constructed substantially symmetrically about the rotation axis CL1, so that its lower half (that is located on a lower side of the rotation axis CL1) is not shown in FIG. 4 .

The transfer 28 further includes a second output shaft 72 and a driven gear 74 which are provided inside the transfer case 44 as the non-rotary member and which are disposed on a common axis in the form of a rotation axis CL2. The driven gear 74 is constructed substantially symmetrically about the rotation axis CL2, so that its upper half (that is located on an upper side of the rotation axis CL2) is not shown in FIG. 4 . The rotation axis CL2 corresponds to an axis of the second output shaft 72, for example.

The transfer 28 further includes the TF rotary electric machine MGF, a pair of connection gears 76 and a chain 78 that are provided inside the transfer case 44 as the non-rotary member. The pair of connection gears 76 consists of a TF rotary-electric-machine connection gear 76 a that is to be rotated integrally with a rotor shaft 80 of the TF rotary electric machine MGF, and a TF counter gear 76 b that constantly meshes with the TF rotary-electric-machine connection gear 76 a. The chain 78 is a member connecting between the drive gear 70 and the driven gear 74.

The transfer 28 further includes a switch actuator 82 (see FIG. 1 ) fixed to the transfer case 44. The switch actuator 82 is an actuator provided to operate the first and second dog clutches D1, D2.

Each of the TF clutch CF1 and the TF brake BF1 is a known wet-type hydraulically-operated frictional engagement device constituted by a multiple-disc type or single-disc type clutch that is to be pressed by a hydraulic actuator. A controlled state of the TF clutch CF1 is switched with change of a CF1 torque Tcfl that is a torque capacity of the TF clutch CF1, wherein the change of the CF1 torque Tcfl is made by a CF1 pressure PRcfl that is a hydraulic pressure of the TF clutch CF1 supplied and regulated by the hydraulic control unit 60. Similarly, a controlled state of the TF brake BF1 is switched with change of a BF1 torque Tbfl that is a torque capacity of the TF brake BF1, wherein the change of the BF1 torque Tbfl is made by a BF1 pressure PRbfl that is a hydraulic pressure of the TF brake BF1 supplied and regulated by the hydraulic control unit 60. Each of the first and second dog clutches D1, D2 is a known dog clutch, i.e., a known claw clutch. With the switch actuator 82 being controlled by the electronic control device 130 that is described below, the controlled state of each of the first and second dog clutches D1, D2 is switched.

The TF input shaft 62 is connected to the transmission output shaft 54 in a power transmittable manner. The first output shaft 66 is connected to the rear propeller shaft 32 in a power transmittable manner. Thus, the first output shaft 66 is configured to output the power inputted thereto to the rear wheels 16 via the rear propeller shaft 32, for example. To the first output shaft 66, the power outputted from the turbine impeller 48 b of the torque converter 48 is to be inputted via the automatic transmission 50, for example. It is noted that the automatic transmission 50 and the transfer 28 cooperate with each other to define a first power transmission path L1 (see FIGS. 2 and 4 ) from the turbine impeller 48 b of the torque converter 48 to the first output shaft 66. The first power transmission path L1 is configured to transmit therethrough the power from the turbine impeller 48 b to the first output shaft 66.

The second output shaft 72 is connected to the pair of front wheels 14 in a in a power transmittable manner, via the front propeller shaft 30, front differential device 34 and pair of front drive shafts 38, so that the power inputted to the second output shaft 72 is outputted to the front wheels 14. The TF counter gear 76 b is fixed to the intermediate shaft 68, unrotatably relative to the intermediate shaft 68. The TF rotary electric machine MGF is connected to the second output shaft 72 in a power transmittable manner, via the rotor shaft 80, pair of connection gears 76, intermediate shaft 68, differential device 64, drive gear 70, chain 78 and driven gear 74, so that the power of the TF rotary electric machine MGF is outputted to the front wheels 14 via the second output shaft 72. It is noted a power transmission path from the TF rotary electric machine MGF to the front wheels 14 constitutes a second power transmission path L2 (see FIG. 1 ) configured to transmit therethrough the power from the TF rotary electric machine MGF to the front wheels 14. The first and second power transmission paths L1, L2 consist of respective routes that are different from each other, namely, are other than each other.

The differential device 64 is constituted by a single-pinion-type planetary gear device, and includes a sun gear S, a carrier CA and a ring gear R. The sun gear S is fixed to the intermediate shaft 68, unrotatably relative to the intermediate shaft 68, so that the TF rotary electric machine MGF is connected to the sun gear S via the pair of connection gears 76. The carrier CA is connected to the drive gear 70, so that the second output shaft 72 is connected to the carrier CA via the drive gear 70, chain 78 and driven gear 74. The ring gear R is selectively connected to the transfer case 44 via the TF brake BF1. The sun gear S and the carrier CA are selectively connected to each other via the TF clutch CF1 that corresponds to “first engagement device” recited in the appended claims. The TF brake BF1, via which the ring gear R is selectively connected to the transfer case 44, corresponds to “second engagement device” recited in the appended claims.

The first dog clutch D1 includes first dog teeth a1, second dog teeth a2, third dog teeth a3 and a first sleeve d1 s. The first dog teeth a1 is fixed to the TF input shaft 62, unrotatably relative to the TF input shaft 62. The second dog teeth a2 is fixed to the first output shaft 66, unrotatably relative to the first output shaft 66. The third dog teeth a3 is fixed to the intermediate shaft 68, unrotatably relative to the intermediate shaft 68. The first sleeve d1 s is movable relative to the first, second and third dog teeth a1, a2, a3, in a direction of the rotation axis CL1, i.e., in a direction parallel to the rotation axis CL1. The first sleeve d1 s has inner circumferential teeth that can mesh with the first, second and third dog teeth a1, a2, a3, so as to be unrotatable relative to the TF input shaft 62, first output shaft 66 and intermediate shaft 68. With the first sleeve d1 s being moved in the direction of the rotation axis CL1 by operation of the switch actuator 82, the first sleeve d1 s is engaged with or released from the first, second and third dog teeth a1, a2, a3. When the first dog clutch D1 is placed in a first state [1] (see FIG. 4 ), the first sleeve d1 s is engaged with the first dog teeth a1 and the second dog teeth a2 whereby the first and second dog teeth a1, a2 are connected to each other. When the first dog clutch D1 is placed in a second state [2] (see FIG. 4 ), the first sleeve d1 s is engaged with the first dog teeth a1 and the third dog teeth a3 whereby the first and third dog teeth a1, a3 are connected to each other. It is noted that FIG. 4 shows the first sleeve d1 s when the first sleeve d1 s is placed in each of the first state [1] and the second state [2], for convenience of description.

The second dog clutch D2 includes fourth dog teeth a4, fifth dog teeth a5, sixth dog teeth a6 and a second sleeve d2 s. The fourth dog teeth a4 is fixed to the ring gear R. The fifth dog teeth a5 is fixed to the carrier CA. The sixth dog teeth a6 is fixed to the first output shaft 66, unrotatably relative to the first output shaft 66. The second sleeve d2 s is movable relative to the fourth, fifth and sixth dog teeth a4, a5, a6, in the direction of the rotation axis CL1. The second sleeve d2 s has inner circumferential teeth that can mesh with the fourth, fifth and sixth dog teeth a4, a5, a6, so as to be unrotatable relative to the ring gear R, carrier CA and first output shaft 66. With the second sleeve d2 s being moved in the direction of the rotation axis CL1 by operation of the switch actuator 82, the second sleeve d2 s is engaged with or released from the fourth, fifth and sixth dog teeth a4, a5, a6. When the second dog clutch D2 is placed in a first state [1] (see FIG. 4 ), the second sleeve d2 s is not engaged with any one of the fourth, fifth and sixth dog teeth a4, a5, a6 so that a neutral state is established with any one of the fourth, fifth and sixth dog teeth a4, a5, a6 being not connected to the others of the fourth, fifth and sixth dog teeth a4, a5, a6. When the second dog clutch D2 is placed in a second state [2] (see FIG. 4 ), the second sleeve d2 s is engaged with the fourth dog teeth a4 and the sixth dog teeth a6 whereby the fourth and sixth dog teeth a4, a6 are connected to each other so that the first output shaft 66 is connected to the ring gear R via the second dog clutch D2 that is placed in the second state [2]. When the second dog clutch D2 is placed in a third state [3] (see FIG. 4 ), the second sleeve d2 s is engaged with the fifth dog teeth a5 and the sixth dog teeth a6 whereby the fifth and sixth dog teeth a5, a6 are connected to each other. It is noted that FIG. 4 shows the second sleeve d2 s when the second sleeve d2 s is placed in each of the first state [1], second state [2] and third state [3], for convenience of description.

FIG. 5 is a collinear chart indicating a relationship among rotational speeds of rotary elements of the transfer 28. In FIG. 5 , three vertical lines Y1, Y2, Y3 corresponding to the three rotary elements of the differential device 64 constituting the transfer 28 are an axis representative of a rotational speed of the sun gear S corresponding to a first rotary element RE1, an axis representative of a rotational speed of the carrier CA corresponding to a second rotary element RE2, and an axis representative of a rotational speed of the ring gear R corresponding to a third rotary element RE3, in order from the left side. Further, in FIG. 5 , a vertical line Y0, which is located on a left side of the vertical line Y1, is an axis representative of a rotational speed of the first output shaft 66 corresponding to an input/output rotary element REIO.

As shown in the collinear chart of FIG. 5 , in the transfer 28, the input/output rotary element REIO is selectively connected to the TF input shaft 62 via the first dog clutch D1 that is placed in the first state [1], and is connected to the rear propeller shaft 32. The first power source PU1 including the engine 12 is connected to the TF input shaft 62 via the hybrid transmission 26 in a power transmittable manner. Further, in the differential device 64, the first rotary element RE1 is connected to the TF rotary electric machine MGF in a power transmittable manner, and is selectively connected to the TF input shaft 62 via the first dog clutch D1 that is placed in the second state [2]. The second rotary element RE2 is connected to the second output shaft 72 (that corresponds to “one of the first and second output shafts” recited in the appended claims), i.e., the front propeller shaft 30, and is selectively selected to the first output shaft 66, i.e., the rear propeller shaft 32, via the second dog clutch D2 that is placed in the third state [3]. The third rotary element RE3 is selectively connected to the first output shaft 66 (that corresponds to “the other of the first and second output shafts” recited in the appended claims) via the second dog clutch D2 that is placed in the third state [2], and is selectively connected to the transfer case 44 via the TF brake BF1. Moreover, the first and second rotary elements RE1, RE2 are selectively connected to each other via the TF clutch CF1. In the collinear chart of FIG. 5 , the relationship among the rotational speeds of the respective first, second and third rotary elements RE1, RE2, RE3 in the differential device 64 is represented by a straight line Lcd. The first output shaft 66 is an output shaft to which the power of the first power source PU1 is to be inputted via the torque converter 48 and from which the power is to be outputted to the rear wheels 16. The second output shaft 72 is an output shaft from which the power is to be outputted to the front wheels 14.

In the differential device 64, when the TF clutch CF1 is in the engaged state and the TF brake BF1 is in the released state, the first, second and third rotary elements RE1, RE2, RE3 are rotatable integrally with one another. On the other hand, in the differential device 64, when the TF clutch CF1 is in the released state and the TF brake BF1 is in the engaged state, the rotational speed of the second rotary element RE2 is made lower than the rotational speed of the first rotary element RE1. Therefore, the differential device 64 serves as a speed change device configured to establish a selected one of a high-speed gear position and a low-speed gear position, wherein the high-speed gear position is established with the TF clutch CF1 being placed in the engaged state, and the low-speed gear position is established with the TF brake BF1 being placed in the engaged state. That is, it is possible to change the rotational speed of the TF rotary electric machine MGF, with the differential device 64 being operated as the speed change device. When establishing the high-speed gear position, the differential device 64 provides a lower gear ratio γtr that is 1.0. When establishing the low-speed gear position, the differential device 64 provides a higher gear ratios γtr that is higher than 1.0. The differential device 64 is provided in the second power transmission path L2.

The differential device 64 is capable of activating a differential effect when both of the F clutch CF1 and the TF brake BF1 being are in the released states. Thus, the differential device 64 serves as a center differential. In this instance, with the first dog clutch D1 being in the first state [1] and with the second dog clutch D2 being in the second state [2] in the transfer 28, the differential device 64 can cause the torque of the first power source PU1 inputted to the third rotary element RE3, to be distributed to the second rotary element RE2, owing a reaction torque of the TF rotary electric machine MGF connected to the first rotary element RE1. Further, the differential device 64 can cause the torque of the first power source PU1 inputted to the third rotary element RE3, to be distributed to the second rotary element RE2, also by limiting the differential effect of the differential device 64 by placing the TF clutch CF1 in a slipping state, in place of applying the reaction torque of the TF rotary electric machine MGF. Thus, the transfer 28 is a torque distribution device configured to distribute a part of the torque inputted to the first output shaft 66, to the second output shaft 72, for thereby making it possible to distribute the torque between the front wheels 14 and the rear wheels 16. It is noted that, in the transfer 28, when the second dog clutch D2 is in the third state [3], the differential device 64 is placed in a differential lock state in which the differential device 64 does not function as the center differential.

FIG. 6 is a table indicating a relationship between each mode established in the transfer 28 and controlled states of respective the engagement devices in the transfer 28. In FIG. 6 , “◯” in columns of the TF brake BF1 and the TF clutch CF1 indicates that the TF brake BF1 or TF clutch CF1 is in its engaged state, and blank in the columns of the TF brake BF1 and the TF clutch CF1 indicates that the TF brake BF1 or TF clutch CF1 is in its released state. Further, in FIG. 6 , “◯” in columns of the first and second dog clutches D1, D2 indicates that the first dog clutch D1 or second dog clutch D2 is placed in the corresponding state, and “(0)” in the column of the first dog clutch D1 indicates that the first dog clutch D1 may be placed in its released state where the first dog clutch D1 can be placed in the released state.

FIG. 6 shows six modes numbered from m1 to m6. Each of “EV (FF) HIGH” mode of number m1 and “EV (FF) LOW” mode of number m2 is established with a corresponding one of the TF clutch CF1 and the TF brake BF1 being placed in the engaged state and with the first and second dog clutches D1, D2 being placed in the respective first states [1]. Each of the “EV (FF) HIGH” mode and the “EV (FF) LOW” mode is a BEV driving mode that enables a motor running (=BEV running) in which the vehicle 8 runs, for example, with only the TF rotary electric machine MGF serving as the power source and with operation of the first power source PU1 being stopped. With the second dog clutch D2 being placed in the first state [1], the neutral state (see “N” in FIG. 6 ) is established with any one of the fourth, fifth and sixth dog teeth a4, a5, a6 being not connected to the others of the fourth, fifth and sixth dog teeth a4, a5, a6, so that a power transmission path between the differential device 64 and the rear wheels 16 is cut off. In this state in which the second dog clutch D2 being placed in the first state [1], the power of the TF rotary electric machine MGF is transmitted toward the front wheels 14 in the differential device 64 in which the high-speed gear position is established with the TF clutch CF1 being in the engaged state or the low-speed gear position is established with the TF brake BF1 being in the engaged state. Thus, in the present embodiment, the BEV running is performed by a front-wheel drive running. In the BEV driving mode, it is possible to avoid drag of the engine 12, for example, with the automatic transmission 50 being placed in the neutral state when the first dog clutch D1 is in the first state [1]. Where the first dog clutch D1 can be placed in the released state, it is possible to avoid drag of the engine 12 and drag of the automatic transmission 50, with the first dog clutch D1 being placed in the released state, even without the automatic transmission 50 being placed in the neutral state. Further, in the BEV driving mode that is the “EV (FF) HIGH” mode or “EV (FF) LOW” mode, the power of the first power source PU1 can be transmitted to the rear wheels 16, for example, with the first dog clutch D1 being placed in the first state [1], so that it is possible to perform an engine running, i.e., a hybrid running (=HEV running) in which the vehicle 8 runs with at least the engine 12 serving as the power source. In this engine running, for example, an AWD running by a parallel hybrid running or a rear-wheel drive running by only the power of the first power source PU1 can be performed.

“H4-TORQUE SPLIT” mode of number m3 is established with both of the TF clutch CF1 and the TF brake BF1 being placed in the respective released states and with the first dog clutch D1 and the second dog clutch D2 being placed in the first state [1] and the second state [2], respectively. The “H4_TORQUE SPLIT” mode is a mode for distributing the torque between the front wheels 14 and the rear wheels 16 at a desired ratio that is dependent on the reaction torque of the TF rotary electric machine MGF, for example, with the torque of the first power source PU1 transmitted from the first output shaft 66 to the differential device 64 being held by the sun gear S to which the reaction torque of the TF rotary electric machine MGF is applied, and with the differential device 64 being placed in a state corresponding to the high-speed gear position. In the “H4_TORQUE SPLIT” mode established in the transfer 28, the TF rotary electric machine MGF performs a power driving.

“H4_LSD” mode of number m4 is established with the TF clutch CF1 being controlled in the slipping state and the TF brake BF1 being placed in the released state, and with the first dog clutch D1 and the second dog clutch D2 being placed in the first state [1] and the second state [2], respectively. The “H4_LSD” mode is a mode for distributing the torque between the front wheels 14 and the rear wheels 16 at a desired ratio that is dependent on the torque capacity of the TF clutch CF1, by limiting the differential effect of the differential device 64 by placing the TF clutch CF1 in the slipping state, in place of applying the reaction torque of the TF rotary electric machine MGF in the “H4_TORQUE SPLIT” mode.

“H4_Lock” mode of number m5 is established with both of the TF clutch CF1 and the TF brake BF1 being placed in the respective released states and with the first dog clutch D1 and the second dog clutch D2 being placed in the first state [1] and the third state [3], respectively. The “H4_Lock” mode is a mode for distributing the torque of the first power source PU1 transmitted to the first output shaft 66, between the front wheels 14 and the rear wheels 16, with the differential device 64 being placed in the differential lock state.

“L4_Lock” mode of number m6 is established with the TF clutch CF1 and the TF brake BF1 being placed in the released state and the engaged state, respectively and with the first dog clutch D1 and the second dog clutch D2 being placed in the second state [2] and the third state [3], respectively. The “L4_Lock” mode is a mode for distributing the torque of the first power source PU1 transmitted to the sun gear S of the differential device 64, between the front wheels 14 and the rear wheels 16, with the differential device 64 being placed in the differential lock state and with the differential device 64 being placed in the low-speed gear position.

Referring back to FIG. 1 , the vehicle driving apparatus 10 includes an MOP 84 that is a mechanically-operated oil pump, an EOP 86 that is an electrically-operated oil pump, and a pump motor 88. The MOP 84 is connected to the connection shaft 46 (see FIG. 2 ), and is to be driven and rotated by the first power source PU1, so as to output a working fluid OIL that is to be used in the power transmission apparatus 18. The pump motor 88 is a motor serving exclusively to drive and rotate the EOP 86. The EOP 86 outputs the working fluid OIL, when being driven and rotated by the pump motor 88. The working fluid OIL outputted by the MOP 84 and the EOP 86 is supplied to the hydraulic control unit 60. The hydraulic control unit 60, which receives the working fluid OIL as an original hydraulic pressure, supplies regulated hydraulic pressures that serve as the CB hydraulic pressure PRcb, the CF1 pressure PRcfl and the BF1 pressure PRbfl, for example.

The vehicle driving apparatus 10 is provided with the electronic control device 130 as a controller including a control device that is configured to control the power sources PU and the transfer 28. FIG. 1 shows an input/output system of the electronic control device 130, and is also a functional block diagram explaining major portions of control functions of the electronic control device 130. The electronic control device 130 includes a so-called microcomputer incorporating a CPU, a ROM, a RAM and an input-output interface. The CPU performs various control operations of the vehicle driving apparatus 10, by processing various input signals, according to control programs stored in the ROM, while utilizing a temporary data storage function of the RAM. The electronic control device 130 may be constituted by two or more control units exclusively assigned to perform respective different control operations such as an engine control operation and a shift control operation.

The electronic control device 130 receives various input signals based on values detected by respective sensors provided in the vehicle driving apparatus 10. Specifically, the electronic control device 130 receives: an output signal of an engine speed sensor 90 indicative of an engine rotational speed Ne that is a rotational speed of the engine 12; an output signal of an MGM speed sensor 92 indicative of an MGM rotational speed Nmgm that is a rotational speed of the TM rotary electric machine MGM, an output signal of a turbine speed sensor 94 indicative of a turbine rotational speed Nt that is equal to the AT input rotational speed Ni; an output signal of an AT output speed sensor 96 indicative of the AT output rotational speed No; an output signal of a vehicle speed sensor 98 indicative of a TF output rotational speed Nof which is a rotational speed of the first output shaft 66 and which corresponds to the vehicle running speed V; an output signal of an MGF speed sensor 100 indicative of an MGF rotational speed Nmgf that is a rotational speed of the TF rotary electric machine MGF; an output signal of an accelerator-opening degree sensor 102 indicative of an accelerator opening degree (accelerator operation degree) θacc representing an amount of accelerating operation made by the vehicle driver; an output signal of a throttle-opening degree sensor 104 indicative of a throttle opening degree θth which is an opening degree of an electronic throttle valve; an output signal of a brake pedal sensor 106 which is a brake-ON signal Bon representing a state in which a brake pedal is being operated by the vehicle driver so as to operate wheel brakes; an output signal of a shift position sensor 108 indicative of a shift operation position POSsh that is an operation position of a shift lever provided in the vehicle 8; an output signal of an acceleration sensor 110 indicative of a longitudinal acceleration Gx and a lateral acceleration Gy of the vehicle 8; an output signal of a yaw rate sensor 112 indicative of a yaw rate Ryaw that is a rotational angular speed of the vehicle 8 about its vertical axis; an output signal of a steering sensor 114 indicative of a steering angle θsw and a steering direction Dsw of a steering wheel provided in the vehicle 8; an output signal of a battery sensor 116 indicative of a battery temperature THbat, a battery charging/discharging electric current That and a battery voltage Vbat of the battery 24; an output signal of a fluid temperature sensor 118 indicative of a working-fluid temperature THoil that is a temperature of the working fluid OIL in the hydraulic control unit 60; an output signal of a differential-lock selection switch 120 which is a lock-mode ON signal LOCKon indicating that the “H4_Lock” mode or “L4_Lock” mode is selected by the vehicle driver; and an output signal of a low-gear selection switch 122 which is a low-gear ON signal LOWon indicating that the low-speed gear position of the differential device 64 is selected by the vehicle driver.

The above-described differential-lock selection switch 120 and low-gear selection switch 122 are provided in vicinity of a driver seat of the vehicle 8. The differential-lock selection switch 120 is a switch that is to be placed in its ON state by the vehicle driver when the differential device 64 is to be placed in the differential lock state in the transfer 28. The low-gear selection switch 122 is a switch that is to be placed in its ON state by the vehicle driver when the differential device 64 is to be placed in the low-speed gear position during the “H4_Lock” mode established in the transfer 28.

The electronic control device 130 generates various output signals to the various devices provided in the vehicle 8, such as: an engine control command signal Se that is to be supplied to the engine control device 20 for controlling the engine 12; an MGM control command signal Smgm that is to be supplied to the inverter 22 for controlling the TM rotary electric machine MGM; an MGF control command signal Smgf that is to be supplied to the inverter 22 for controlling the TF rotary electric machine MGF; a hydraulic command signal Sat that is to be supplied to the hydraulic control unit 60 for controlling the controlled state of each of the engagement devices CB so as to control the automatic transmission 50; a hydraulic command signal Scbf that is to be supplied to the hydraulic control unit 60 for controlling the controlled state of each of the TF clutch CF1 and the TF brake BF1 so as to control the transfer 28; a transfer control command signal Stf that is to be supplied to the switch actuator 82 for operating the first and second dog clutches D1, D2 so as to control the transfer 28; an EOP control command signal Seop that is to be supplied to the pump motor 88 for controlling the EOP 86; a brake control command signal Sb that is to be supplied to a wheel brake device 124 for controlling a braking force generated by each wheel brake; and an information-notification control command signal Sinf that is to be supplied to an information notification device 126 for notifying various information to the vehicle driver.

For performing various control operations in the vehicle driving apparatus 10, the electronic control device 130 includes an AT shift control means in the form of an AT shift control portion 132, a hybrid control means in the form of a hybrid control portion 134 and a drive-state control means in the form of a drive-state control portion 136.

The AT shift control portion 132 determines whether a shifting action is to be executed in the automatic transmission 50, by using an AT-gear-position shifting map shown in FIG. 7 , for example, and outputs the hydraulic command signal Sat, as needed, which is supplied to the hydraulic control unit 60, for executing the shifting action in the automatic transmission 50. The AT-gear-position shifting map represents a predetermined relationship, i.e., a pre-stored relationship obtained by experimentation or determined by an appropriate design theory. In the AT-gear-position shifting map, the predetermined relationship is represented by shifting lines in two-dimensional coordinates in which the vehicle running speed V and a requested drive torque Trdem as two variables are taken along respective two axes, wherein the shifting lines are used for the determination as to whether the shifting action is to be executed in the automatic transmission 50. In the AT-gear-position shifting map, one of the two variables may be the AT output rotational speed No in place of the vehicle running speed V, and the other of the two variables may be any one of a requested drive force Frdem, the accelerator opening degree θacc and the throttle opening degree θth in place of the requested drive torque Trdem. The above-described shifting lines in the AT-gear-position shifting map consist of shift-up lines (indicated by solid lines in FIG. 7 ) for determining a shift-up action of the automatic transmission 50, and shift-down lines (indicated by broken lines in FIG. 7 ) for determining a shift-down action of the automatic transmission 50.

The hybrid control portion 134 has a function serving as an engine control means or portion 134 a for controlling the operation of the engine 12 and a function serving as a rotating-machine control means or portion 134 b for controlling the operations of the TM rotary electric machine MGM and the TF rotary electric machine MGF through the inverter 22, and executes a hybrid drive control, for example, using the engine 12, TM rotary electric machine MGM and TF rotary electric machine MGF through these control functions.

The hybrid control portion 134 calculates a drive request amount requested to the vehicle 8 by the vehicle driver, by applying the accelerator opening degree θacc and the vehicle running speed V to, for example, a drive request amount map that is a predetermined relationship. The drive request amount is, for example, the requested drive torque Trdem [Nm] that is to be applied to the drive wheels. The requested drive force Frdem [N] applied to the drive wheels, a requested drive power Prdem [W] applied to the drive wheels or a requested AT output torque applied to the transmission output shaft 54, for example, can be used as the drive request amount, in addition to or in place of the requested drive torque Trdem. From another point of view, the requested drive torque Trdem corresponds to the requested drive power Prdem at a speed value of the vehicle running speed V upon output of a command signal. In calculation of the drive request amount, the TF output rotational speed Nof may be used in place of the vehicle running speed V.

The hybrid control portion 134 outputs the engine control command signal Se, MGM control command signal Smgm and MGF control command signal Smgf for controlling the engine 12, TM rotary electric machine MGM and TF rotary electric machine MGF, respectively, such that the requested drive power Prdem is realized, by taking account of various factors such as a transmission loss, an auxiliary load, the gear ratio γat of the automatic transmission 50, the currently established gear ratio γtr of the differential device 64 and a maximum chargeable amount Win and a maximum dischargeable amount Wout of the battery 24. The engine control command signal Se is, for example, a command value for realizing a requested engine power Pedem that is a requested value of an engine power Pe for outputting the engine torque Te at a speed value of the engine rotational speed Ne upon output of the engine control command signal Se. The engine power Pe is an output [W] of the engine 12, i.e., a power of the engine 12. The MGM control command signal Smgm is, for example, a command value of a consumed electric power Wcmgm or a generated electric power Wgmgm of the TM rotary electric machine MGM for outputting the MGM torque Tmgm at a speed value of the MGM rotational speed Nmgm upon output of the MGM control command signal Smgm. The MGF control command signal Smgf is, for example, a command value of a consumed electric power Wcmgf or a generated electric power Wgmgf of the TF rotary electric machine MGF for outputting the MGF torque Tmgf at a speed value of the MGF rotational speed Nmgf upon output of the MGF control command signal Smgf.

The maximum chargeable amount Win of the battery 24 is a maximum amount of the electric power that can be charged to the battery 24, and indicates an input limit of the battery 24. The maximum dischargeable amount Wout of the battery 24 is a maximum amount of the electric power that can be discharged from the battery 24, and indicates an output limit of the battery 24. The maximum chargeable and dischargeable amounts Win, Wout are calculated by the electronic control device 130, for example, based on a battery temperature THbat and a charged state value SOC [%] of the battery 24 that corresponds to a stored electric energy amount (charged electric energy amount) of the battery 24. The charged state value SOC of the battery 24 is a value indicative of a charged state of the battery 24, and is calculated by the electronic control device 130, for example, based on the charging/discharging electric current Ibat and the voltage Vbat of the battery 24.

The hybrid control portion 134 establishes a BEV driving mode when the requested drive power Prdem is in a motor drive region smaller than a predetermined threshold value, and establishes an HEV driving mode (in which an engine running of the vehicle 8 can be performed) when the requested drive power Prdem is in an engine drive region not smaller than the predetermined threshold value. In FIG. 7 , one-dot chain line A is a boundary line between the engine drive region and the motor drive region, for switching between the BEV driving mode and the HEV driving mode. A predetermined relationship having the boundary line as indicated by the one-dot chain line A of FIG. 7 is an example of a driving-mode switching map defined by two-dimensional coordinates of variables in the form of the vehicle running speed V and the requested drive torque Trdem. It is noted that, in FIG. 7 , the driving-mode switching map is shown together with the AT-gear-position shifting map, for convenience of the description.

Even when the requested drive power Prdem is in the motor drive region, the hybrid control portion 134 establishes the HEV driving mode, for example, in a case in which the charged state value SOC of the battery 24 becomes less than a predetermined engine-start threshold value or in a case in which the engine 12 needs to be warmed up. From another point of view, the motor drive region disappears in the case in which the charged state value SOC becomes less than the engine-start threshold value or in the case in which the engine 12 needs to be warmed up. The engine-start threshold value is a predetermined threshold value for determining that the charged state value SOC reaches a level at which the battery 24 needs to be charged by automatically starting the engine 12.

The drive-state control portion 136 determines one of the modes (see FIG. 6 ) that is to be established in the transfer 28, based on various factors such as the vehicle running speed V, accelerator opening degree θacc, brake ON signal Bon, shift operation position POSsh, longitudinal acceleration Gx, lateral acceleration Gy, yaw rate Ryaw, steering angle θsw, steering direction Dsw, lock-mode ON signal LOCKon and low-gear ON signal LOWon, and outputs various control command signals required for establishing the determined one of the modes. The various control command signals include the hydraulic command signal Scbf for the TF clutch CF1 and TF brake BF1 and the transfer control command signal Stf for the first and second dog clutches D1, D2.

During the BEV driving mode, the drive-state control portion 136 establishes the low-speed gear position in the differential device 64 by placing the TF brake BF1 and the TF clutch CF1 in the engaged state and the released state, respectively, when the vehicle running speed V is in a relatively low speed range, and establishes the high-speed gear position in the differential device 64 by placing the TF brake BF1 and the TF clutch CF1 in the released state and the engaged state, respectively, when the vehicle running speed V is in a relatively high speed range. That is, during the BEV driving mode, the drive-state control portion 136 establishes the “EV (FF) LOW” mode (i.e., low-speed gear position) when the vehicle running speed V is in the relatively low speed range, and establishes “EV (FF) HIGH” mode (i.e., high-speed gear position) when the vehicle running speed V is in the relatively high speed range.

In each of the “H4_TORQUE SPLIT” mode and the “H4_LSD” mode, the drive-state control portion 136 determines a running state of the vehicle 8, based on the output signals of various sensors such as the vehicle speed sensor 98, acceleration sensor 110 and yaw rate sensor 112, and sets a target value of a torque distribution ratio Rx that is dependent on the determined running state of the vehicle 8. The torque distribution ratio Rx is a ratio of distribution of the torque of the power sources PU, between the front wheels 14 and the rear wheels 16. The torque distribution ratio Rx may be represented by a rear-wheel-side distribution ratio Xr that is a ratio of the torque transmitted to the rear wheels 16 from the power sources PU, to the total toque transmitted to the front and rear wheels 14, 16 from the power sources PU. Alternatively, the torque distribution ratio Rx may be represented by a front-wheel-side distribution ratio Xf (=1−Xr) that is a ratio of the torque transmitted to the front wheels 14 from the power sources PU, to the total toque transmitted to the front and rear wheels 14, 16 from the power sources PU.

In the “H4_TORQUE SPLIT” mode, the drive-state control portion 136 outputs the MGF control command signal Smgf for controlling the TF rotary electric machine MGF such that the rear-wheel-side distribution ratio Xr becomes the target value by adjusting the MGF torque Tmgf of the TF rotary electric machine MGF serving as the above-described reaction torque (that is applied to the sun gear S of the differential device 64). With increase of the MGF torque Tmgf, the rear-wheel-side distribution ratio Xr is reduced, namely, the front-wheel-side distribution ratio Xf is increased. In the “H4_LSD” mode, the drive-state control portion 136 outputs the hydraulic command signal Scbf for controlling the slipping state of the TF clutch CF1 such that the rear-wheel-side distribution ratio Xr becomes the target value by adjusting the torque capacity of the TF clutch CF1. With increase of the torque capacity of the TF clutch CF1, the rear-wheel-side distribution ratio Xr is reduced.

The drive-state control portion 136 establishes the “H4_Lock” mode, when the differential-lock selection switch 120 is placed into the ON state by the vehicle driver in the “H4_TORQUE SPLIT” mode or the “H4_LSD” mode. The drive-state control portion 136 establishes the “L4_Lock” mode, when the low-gear selection switch 122 is placed into the ON state by the vehicle driver in the “H4_Lock” mode during stop of the vehicle 8.

There will be described, with reference to FIG. 8 , an engine operation point PNTeng that can be changed in the vehicle driving apparatus 10, as in a continuously-variable transmission. The engine operation point PNTeng is a driving point or an operation point of the engine 12, which is represented by a combination of the engine rotational speed Ne and the engine torque Te.

In FIG. 8 , each of equal power lines Lope, which are indicated by two-dot chain lines, represents an example of the requested engine power Pedem that realizes the requested drive power Prdem calculated based on, for example, the accelerator opening degree θacc. The requested engine power Pedem is the engine power Pe requested by the accelerating operation or other operation made by the vehicle driver. On the other hand, a broken line LOW represents an example of a pump torque Top that is a torque generated in the pump impeller 48 a depending on a speed ratio e (=Nt/Np) of the torque converter 48, in two-dimensional coordinates in which the engine rotational speed Ne and the engine torque Te as two variables are taken along respective two axes, for convenience of description. A pump rotational speed Np is a rotational speed of the pump impeller 48 a, and is equal to the engine rotational speed Ne. Under a constant value of the turbine rotational speed Nt, the pump torque Top represented by the broken line LOW has a relationship with the engine rotational speed Ne, which is dependent on a hardware construction. When the requested engine power Pedem corresponds to one of the equal power lines Lpe that is indicated by a two-dot chain line L02, for example, the engine operation point PNTeng is naturally set to a so-called coupling point P01 at which the broken line L01 and the two-dot chain line L02 intersect with each other.

The engine operation point PNTeng can be shifted or changed from the coupling point P01 to a fuel-economy optimum point P02 lying on a fuel-economy optimum line Lfl (indicated by solid line L03), while being kept on the above-described one of the equal power lines Lpe that corresponds to the requested engine power Pedem, for example, by using a part of the engine power Pe to cause the TM rotary electric machine MGM to perform a power generation. The fuel-economy optimum line Lfl is a predetermined operation curve representing combinations between values of the engine rotational speed Ne and the engine torque Te, which cooperate with each other to maximize the fuel economy of the engine 12. That is, the fuel-economy optimum line Lfl consists of a succession of predetermined fuel-economy optimum points each of which is an optimum engine operation point PNTeng for improving the fuel economy of the engine 12. In the vehicle driving apparatus 10, it is possible to change the engine operation point PNTeng arbitrarily without being constrained by the turbine rotation speed Nt, by adjusting the MGM torque Tmgm such that a sum of the engine torque Te and the MGM torque Tmgm is balanced with the pump torque Tp, namely, such that a relationship represented by an equation “Tp=Te+Tmgm (that is a negative value in FIG. 8 )” is established. When the MGM torque Tmgm is a negative value, namely, when the TM rotary electric machine MGM is caused to perform the power generation, the electric power generated by the TM rotary electric machine MGM is basically supplied to the TF rotary electric machine MGF and is converted into the mechanical power by the TF rotary electric machine MGF. The vehicle driving apparatus 10 has an electrical path and a mechanical path as power transmission paths of the engine power Pe, wherein the electrical path is a path through which the electric power is to be transmitted or transferred between the TM rotary electric machine MGM and the TF rotary electric machine MGF, while the mechanical path is a path through which the mechanical path is to be transmitted or transferred via the torque converter 48. In the vehicle driving apparatus 10, an electrically-operated continuously-variable transmission is formed with use of the TM rotary electric machine MGM and the TF rotary electric machine MGF.

The hybrid control portion 134 controls the engine operation point PNTeng by adjusting an electrical path amount Ppse [W] that is an amount of the electric power in the electrical path through which the electric power is to be transferred between the TM rotary electric machine MGM and the TF rotary electric machine MGF. The electrical path amount Ppse is, for example, a product of the MGM torque Tmgm and the MGM rotational speed Nmgm.

The hybrid control portion 134 obtains a target electrical path amount Ppsetgt as a target value of the electrical path amount Ppse by which the engine operation point PNTeng is caused to become a target operation point PNTtgt. The target operation point PNTtgt is, for example, the above-described fuel-economy optimum point, and is the fuel-economy optimum point P02 (see FIG. 8 ) when the requested engine power Pedem corresponds to the two-dot chain line L02. The target electrical path amount Ppsetg is a product of the MGM torque Tmgm, which is required to change the engine operation point PNTeng from the coupling point to the fuel-economy optimum point, and the engine rotational speed Ne, i.e., the MGM rotational speed Nmgm, at the fuel-economy optimum point. The hybrid control portion 134 drives the TF rotary electric machine MGF while controlling the MGM torque Tmgm such that the electrical path amount Ppse, which is the amount of the electric power transferred from the TM rotary electric machine MGM to the TF rotary electric machine MGF through the electrical path, becomes the target electrical path amount Ppsetgt. Owing to this arrangement, it is possible to improve a combustion efficiency of the engine 12 while maintaining the same engine power Pe, so that the fuel economy of the engine 12 can be improved.

As described above, in the vehicle driving apparatus 10, the electric power generated by the TM rotary electric machine MGM is supplied through the electrical path to the TF rotary electric machine MGF so that the TF rotary electric machine MGF can be driven. The output characteristic of the TF rotary electric machine MGF is dependent on the MGF rotational speed Nmgf and the MGF torque Tmgf, and the attainable electrical path amount Ppse is limited by the output characteristic of the TF rotary electric machine MGF. Consequently, there is a case in which the engine 12 could not be operated at the fuel-economy optimum point as the operation point, so that there is a room for improvement in the fuel economy of the engine. On the other hand, in the present embodiment, the hybrid control portion 134 calculates the target electrical path amount Ppsetgt that enables the operation point PNTeng of the engine 12 to become the target operation point PNTtgt, and to control the differential device 64 based on the obtained target electrical path amount Ppsetgt so as to establish one of the gear ratios γtr of the differential device 64, which enables the obtained target electrical path amount Ppsetgt to be attainable. Further, the hybrid control portion 134 adjusts the electrical path amount Ppse to the obtained target electrical path amount Ppsetgt, and controls the operation point PNTeng of the engine 12.

The hybrid control portion 134 calculates the requested engine power Pedem of the engine 12 that realizes the requested drive power Prdem calculated based on, for example, the vehicle running speed V and accelerator opening degree θacc. Then, the target operation point PNTtgt is calculated based on relationship shown in FIG. 8 , wherein the target operation point PNTtgt lies on the fuel-economy optimum line, and the requested engine power Pedem can be assured when the engine 12 is operated at the target operation point PNTtgt. Further, after calculating the target operation point PNTtgt of the engine 12, the hybrid control portion 134 calculates the target electrical path amount Ppsetgt that makes it possible to shift the operation point PNTeng of the engine 12 to the target operation point PNTtgt.

When the calculated target electrical path amount Ppsetgt is to be realized, the drive-state control portion 136 determines whether the differential device 64 can select or establish one of the gear ratios γtr that enables the calculated target electrical path amount Ppsetgt to be attainable, or not. As described above, the differential device 64 serves as a the speed change device that is configured to establish a selected one of the high and low-speed gear positions, depending on which one of the TF brake BF1 and the TF clutch CF1 is placed in the engaged state. The drive-state control portion 136 determines that the differential device 64 can select or establish the one of the gear ratios γtr that enables the calculated target electrical path amount Ppsetgt to be attainable, when the differential device 64 can establish the high-speed gear position and the high-speed gear position that enables the calculated target electrical path amount Ppsetgt to be attainable, or when the differential device 64 can establish the low-speed gear position and the low-speed gear position that enables the calculated target electrical path amount Ppsetgt to be attainable.

FIG. 9 shows, by way of example, a motor characteristic of the TF rotary electric machine MGF, wherein its horizontal axis represents the vehicle running speed V while its vertical axis represents the MGF torque Tmgf of the TF rotary electric machine MGF. In FIG. 8 , solid line represents the motor characteristic when the differential device 64 is in the low-speed gear position, while broken line represents the motor characteristic when the differential device 64 is in the high-speed gear position. As shown in FIG. 9 , the MGF torque Tmgf can be made higher during running of the vehicle 8 in a low running speed range, when the differential device 64 is in the low-speed gear position, as compared with when the differential device 64 is in the high-speed gear position. Further, the MGF torque Tmgf of the TF rotary electric machine MGF can be generated during running of the vehicle 8 in a high running speed range, when the differential device 64 is in the high-speed gear position, as compared with when the differential device 64 is in the low-speed gear position. Further, in FIG. 9 , a region surrounded by the solid line and a region surrounded by broken line overlap with each other in a region A that is represented by diagonal lines. This region A corresponds to a region in which the TF rotary electric machine MGF can be operated irrespective of whether the differential device 64 is placed in the high-speed gear position or the low-speed gear position. In other words, the region A corresponds to a region in which both of two gear ratios γtr are selectable in the differential device 64. Further, a region B, which is surrounded by the solid line and is not surrounded by the broken line, is a region in which the TF rotary electric machine MGF can be operated with the differential device 64 being placed in the low-speed gear position. Still further, a region C, which is surrounded by the broken line and is not surrounded by the solid line, is a region in which the TF rotary electric machine MGF can be operated with the differential device 64 being placed in the high-speed gear position.

Therefore, in a case in which the operation point of the TF rotary electric machine MGF is in the region A when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, namely, when the target electrical path amount Ppsetgt is to be completely consumed by the TF rotary electric machine MGF, the target electrical path amount Ppsetgt is attainable irrespective of whether the differential device 64 is in the low-speed gear position providing a higher gear ratio γtrlow or is in the high-speed gear position providing a lower gear ratio γtrhi (that is lower than the higher gear ratio γtrlow). In a case in which the operation point of the TF rotary electric machine MGF is in the region B when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the target electrical path amount Ppsetgt becomes attainable by placing the differential device 64 into the low-speed gear position providing the higher gear ratio γtrlow. In a case in which the operation point of the TF rotary electric machine MGF is in the region C when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the target electrical path amount Ppsetgt becomes attainable by placing the differential device 64 into the high-speed gear position providing the lower gear ratio γtrhi.

Thus, in the case in which the operation point of the TF rotary electric machine MGF is in the region A when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the drive-state control portion 136 determines that at least two of the gear ratios γtr (both of the higher gear ratio γtrlow and the lower gear ratio γtrhi in the present embodiment) enable the target electrical path amount Ppsetgt to be attainable. In the case in which the operation point of the TF rotary electric machine MGF is in the region B when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the drive-state control portion 136 determines that one of the gear ratios γtr, specifically, only the higher gear ratio γtrlow provided by the low-speed gear position, enables the target electrical path amount Ppsetgt to be attainable. In the case in which the operation point of the TF rotary electric machine MGF is in the region C when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the drive-state control portion 136 determines that one of the gear ratios γtr, specifically, only the lower gear ratio γtrhi provided by the high-speed gear position, enables the target electrical path amount Ppsetgt to be attainable.

In the above-described case in which at least two of the gear ratios γtr enable the target electrical path amount Ppsetgt to be attainable, the drive-state control portion 136 selects one out of the at least two of the gear ratios γtr, which maximizes a motor efficiency (electricity cost efficiency), namely, one out of the at least two of the gear ratios γtr, which makes the motor efficiency better than the other of the at least two of the gear ratios γtr. In FIG. 9 , a plurality of solid lines Lep1, which are described in a layered manner, are equal efficiency lines (equal electricity-cost lines) in a case in which the differential device 64 is placed in the low-speed gear position providing the higher gear ratio γtrlow. That is, each of the solid lines Lep1 described in the layered manner is a succession of points at which the same motor efficiency ηmotor is obtained. Further, in FIG. 9 , a plurality of broken lines Lep2, which are described in a layered manner, are equal efficiency lines (equal electricity-cost lines) in a case in which the differential device 64 is placed in the high-speed gear position providing the lower gear ratio γtrhi. That is, each of the broken lines Lep2 described in the layered manner is a succession of points at which the same motor efficiency ηmotor is obtained. Still further, the motor efficiency ηmotor is higher on each one of the equal efficiency lines Lep1, which is located inside the others of the equal efficiency lines Lep1, than on the others of the equal efficiency lines Lep1, in FIG. 9 . Similarly, the motor efficiency ηmotor is higher on each one of the equal efficiency lines Lep2, which is located inside the others of the equal efficiency lines Lep2, than on the others of the equal efficiency lines Lep2, in FIG. 9 . Moreover, in FIG. 9 , one-dot chain line represents an equal power line, for example, where the output (power) of the TF rotary electric machine MGF is an output P1 (power P1). This output P1 is equivalent to the target electrical path amount Ppsetgt. That is, the output P1 corresponds to a motor power by which the target electrical path amount Ppsetgt can be attained.

In FIG. 9 , in a case in which the vehicle running speed V is a running speed V1, an intersection point F (operation point F) between the equal power line representing the output P (practically, target electrical path amount Ppsetgt) and a vertical line representing the running speed V1 is the operation point PNTmgf of the TF rotary electric machine MGF. In this case, the operation point F is in the region A, so that the target electrical path amount Ppsetgt is attainable irrespective of whether the differential device 64 is in the low-speed gear position providing the higher gear ratio γtrlow or is in the high-speed gear position providing the lower gear ratio γtrhi, so that one of the higher gear ratio γtrlow and the lower gear ratio γtrhi, which makes the motor efficiency ηmotor of the TF rotary electric machine MGF higher than the other, is selected. In this case in which the operation point PNTmgf of the TF rotary electric machine MGF is the operation point F when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the operation point F is located in an inner position in a group of the equal efficiency lines Lep1 (represented by the solid lines), rather than in a group of the equal efficiency lines Lep2 (represented by the broken lines), as shown in FIG. 9 , so that the motor efficiency ηmotor is made higher when the differential device 64 is placed in the low-speed gear position providing the higher gear ratio γtrlow than when the differential device 64 is placed in the high-speed gear position providing the lower gear ratio γtrhi. In this instance, the drive-state control portion 136 selects the low-speed gear position providing the higher gear ratio γtrlow in the differential device 64, and executes a shifting action, as needed, so as to establish the higher gear ratio γtrlow in the differential device 64. Thus, when at least two of the plurality of gear ratios γtr enable the target electrical path amount Ppsetgt to be attainable, the drive-state control portion 136 is configured to cause the differential device 64 to establish one of the at least two of the gear ratios γtr that maximizes the motor efficiency ηmotor of the TF rotary electric machine MGF. Thus, it is possible to improve the motor efficiency ηmotor during operation of the TF rotary electric machine MGF and to reduce an amount of electric power consumption during operation of the TF rotary electric machine MGF.

On the other hand, in a case in which the operation point PNTmgf of the TF rotary electric machine MGF is in the region B or the region C that are shown in FIG. 9 when the target electrical path amount Ppsetgt is to be attained by the TF rotary electric machine MGF, the drive-state control portion 136 establishes one of the gear ratios γtr that enables the target electrical path amount Ppsetgt to be attainable. Consequently, the engine 12 can be operated at the operation point PNTeng that lies on the fuel-economy optimum line, thereby improving the fuel economy during running of the vehicle 8.

FIG. 10 is a flow chart showing a main part of a control routine that is to be executed by the electronic control device 130, for improving the fuel economy, by appropriately controlling the operation point PNTeng of the engine 12 by selecting a suitable one of gear ratios γtr of the differential device 64 during running of the vehicle 8. This control routine is executed during the HEV running of the vehicle 8, in a repeated manner, wherein the HEV running is running of the vehicle 8 with the transfer 28 being placed in the “EV (FF) HIGH” mode or the “EV (FF) LOW” mode.

The control routine is initiated with step S10 corresponding to control function of the hybrid control portion 134, which is implemented to calculate the requested engine power Pedem, for example, based on the vehicle running speed V and the accelerator opening degree θacc, and to calculate the target operation point PNTtgt of the engine 12 that realizes the requested engine power Pedem. Further, at step S10, the target electrical path amount Ppsetgt, which is required for operating the engine 12 at the calculated target operation point PNTtgt, is calculated. Then, at step S20 corresponding to control function of the drive-state control portion 136, it is determined whether the gear ratios γtr of the differential device 64 are selectable or not, namely, whether at least two of the gear ratios γtr enable the target electrical path amount Ppsetgt to be attainable or not. When an affirmative determination is made at step S20, step S30 corresponding to control function of the drive-state control portion 136 is implemented to select one of the at least two of the gear ratios γtr that maximizes the motor efficiency ηmotor of the TF rotary electric machine MGF. When a negative determination is made at step S20, the control flow goes to step S40 corresponding to control function of the drive-state control portion 136, which is implemented to select one of the gear ratios γtr of the differential device 64 that enables the target electrical path amount Ppsetgt to be attainable. Then, at step S50 corresponding to control function of the drive-state control portion 136, the shifting action is executed in the differential device 64 such that the selected one of the gear ratios γtr (that is selected at step S30 or step S40) is established in the differential device 64. Step S50 is followed by step S60 corresponding to control function of the hybrid control portion 134, which is implemented to control the engine 12 such that the engine 12 is operated at the operation point PNTeng that enables the target electrical path amount Ppsetgt to be attainable.

As described above, in the present embodiment, the electronic control device 130 is configured to obtain the target electrical path amount Psetgt that enables the operation point PNTeng of the engine 12 to become the target operation point PNTtgt, and to control the differential device 64 based on the obtained target electrical path amount Psetgt so as to establish one of the gear ratios γtr that enables the obtained target electrical path amount Psetgt to be attainable, and the electronic control device 130 is configured to adjust the electrical path amount Ppse to the obtained target electrical path amount Psetgt, and to control the operation point PNTeng of the engine 12. Thus, it is possible to restrain the electrical path amount Ppse from being limited by the output characteristic of the TF rotary electric machine MGF. Consequently, the engine 12 can be operated at the operation point PNTeng that improves the fuel economy of the engine 12.

In the present embodiment, when at least two of the gear ratios γtr of the differential device 64 enable the obtained target electrical path amount Psetgt to be attainable, the electronic control device 130 is configured to cause the differential device 64 to establish one of the at least two of the gear ratios γtr that maximizes the efficiency of the TF rotary electric machine MGF. It is therefore possible to improve an efficiency of the electrical path. Further, the speed change device is constructed to include the differential device 66 constituting the torque distribution device, so that it is possible to suppress increase the number of components required for the speed change device.

There will be described other embodiments of this invention. The same reference signs as used in the above-described first embodiment will be used in the following embodiment, to identify the functionally corresponding elements, and descriptions thereof are not provided.

Second Embodiment

In the above-described first embodiment, it is assumed that the shifting action is always executable in the differential device 64. However, there is a case in which the shifting action is disabled in the differential device 64, for example, due to failure of an electromagnetic valve that is to be operated for the shifting action, or a case in which the shifting action is inhibited in the differential device 64, for example, for preparation for transition from a running mode to another running mode. Therefore, in such a case, the target electrical path amount Ppsetgt could be unattainable, depending on one of the gear positions that is established when the shifting action becomes unexecutable in the differential device 64. In the present second embodiment, in an event that the shifting action for switching a currently established one of the gear ratios γtr to another one of the gear ratios γtr becomes unexecutable, a hybrid control portion 154 (see FIG. 1 ) limits the electrical path amount Ppse depending on the currently established one of the gear ratios γtr.

A drive-state control portion 156 (see FIG. 1 ) determines whether the shifting action is unexecutable in the differential device 64 or not, namely, the differential device 64 is in a gear-ratio fixed state in which a currently established gear position cannot be switched to another gear position, or not. The drive-state control portion 156 determines whether the differential device 64 is in the gear-ratio fixed state or not, depending on whether at least one of the electromagnetic valves to be operated for the shifting action is in a failure state, and/or depending on whether the differential device 64 is in preparation for transition from a running mode to another running mode. When determining that the shifting action is executable in the differential device 64, the drive-state control portion 156 executes substantially the same control operations as in the above-described first embodiment, namely, executes the shifting action, as needed, for establishing one of the gear ratios γtr that enables the target electrical path amount Ppsetgt to be attainable. On the other hand, when it is determined by the drive-state control portion 156 that the shifting action is unexecutable in the differential device 64, the hybrid control portion 154 obtains an allowable electrical path amount Ppseper that is attainable in the currently established one of the gear ratios γtr of the differential device 64. The allowable electrical path amount Ppseper can be obtained, for example, by applying the currently established gear ratio γtr of the differential device 64 and the vehicle running speed V to the motor characteristic of the TF rotary electric machine MGF that is shown in FIG. 9 . Then, the hybrid control portion 154 determines whether the obtained allowable electrical path amount Ppseper is at least the target electrical path amount Ppsetgt or not, namely, whether the target electrical path amount Ppsetgt is attainable in the currently established one of the gear ratios γtr of the differential device 64. When the allowable electrical path amount Ppseper is not smaller than the target electrical path amount Ppsetgt, the target electrical path amount Ppsetgt is attainable even in the currently established one of the gear ratios γtr of the differential device 64, so that the hybrid control portion 154 controls the engine 12, the TM rotary electric machine MGM and the TF rotary electric machine MGF such that the engine 12 is operated at the operation point PNTeng that lies on the fuel-economy optimum line, without limiting the electrical path amount Ppse.

On the other hand, when the allowable electrical path amount Ppseper is smaller than the target electrical path amount Ppsetgt, the hybrid control portion 154 limits the electrical path amount Ppse to the allowable electrical path amount Ppseper that is currently attainable. As a result of the limitation of the electrical path amount Ppse to the allowable electrical path amount Ppseper, the MGM torque Tmgm (regenerative torque) of the TM rotary electric machine MGM is reduced and accordingly the operation point PNTeng of the engine 12 is deviated from the fuel-economy optimum line by an amount corresponding to the limitation or reduction of the MGM torque Tmgm. Specifically, as shown in FIG. 8 , in contrast to the case in which the engine 12 is operated at the fuel-economy optimum point P02 with the MGM torque Tmgm being generated by the TM rotary electric machine MGM, the operation point PNTeng of the engine 12 is changed to an operation point P03 so as to be deviated from the fuel-economy optimum point P02, as the result of the limitation of the electrical path amount Ppse to the allowable electrical path amount Ppseper. With the engine 12 being operated at the operation point P03, the MGM torque Tmgm of the TM rotary electric machine MGM is limited to an MGM torque Tmgm1, which is smaller than the MGM torque Tmgm when the engine 12 is operated at the fuel-economy optimum point P02. Thus, when the shifting action is disabled in the differential device 64 and currently established and the target electrical path amount Ppsetgt is hard to be attained in the currently established one of the gear ratios γtr of the differential device 64, the electrical path amount Ppse is limited to the allowable electrical path amount Ppseper that is attainable in the current situation, namely, in the currently established one of the gear ratios γtr of the differential device 64. Owing to this control arrangement, although the operation point PNTeng of the engine 12 is deviated from the fuel-economy optimum point P02, it is possible to minimize an amount of deviation of the operation point PNTeng of the engine 12 from the fuel-economy optimum point P02 and accordingly to suppress the reduction of the fuel economy which is caused by the deviation of the operation point PNTeng of the engine 12 from the fuel-economy optimum point P02.

FIG. 11 is a flow chart showing a main part of a control routine that is to be executed by an electronic control device 150 (see FIG. 1 ), for improving the fuel economy of the engine 12, by appropriately setting the electrical path amount Ppse in a state in which the gear position of the differential device 64 is fixed. This control routine is executed during the HEV running of the vehicle 8, in a repeated manner, like the control routine show in the flow chart of FIG. 10 .

The control routine is initiated with step S100 corresponding to control function of the hybrid control portion 154, which is implemented to calculate the requested engine power Pedem, for example, based on the vehicle running speed V and the accelerator opening degree θacc, and to calculate the target operation point PNTtgt of the engine 12 that realizes the requested engine power Pedem. Further, at step S100, the target electrical path amount Ppsetgt, which is required for operating the engine 12 at the calculated target operation point PNTtgt, is calculated. Step S100 is followed by step S110 corresponding to control function of the drive-state control portion 156, which is implemented to determine whether the shifting action is unexecutable in the differential device 64 or not, namely, the differential device 64 is in the gear-ratio fixed state in which the currently established gear position cannot be switched to another gear position, or not. When a negative determination is made at step S110, namely, when the currently established gear position can be switched to another gear position, the control flow goes to step S150 corresponding to control functions of the hybrid control portion 154 and drive-state control portion 156, which is implemented to control such that the operation point PNTeng of the engine 12 lies on the fuel-economy optimum line. Specifically, step S150 is implemented to execute substantially the same control operations as in the above-described first embodiment. When an affirmative determination is made at step S110, step S120 corresponding to control function of the hybrid control portion 154 is implemented to obtain the allowable electrical path amount Ppseper that is attainable in the currently established one of the gear ratios γtr of the differential device 64, and to determine whether the target electrical path amount Ppsetgt is attainable or not, depending on whether the obtained allowable electrical path amount Ppseper is at least the target electrical path amount Ppsetgt or not. When an affirmative determination is made at step S120, the control flow goes to step S150 that is implemented to control the engine 12 such that the operation point PNTeng lies on the fuel-economy optimum line. When a negative determination is made at step S120, step S130 corresponding to control function of the hybrid control portion 154 is implemented to limit the electrical path amount Ppse to the allowable electrical path amount Ppseper that is attainable in the current situation. At step S140 corresponding to control function of the hybrid control portion 154, since the electrical path amount Ppse is limited to the allowable electrical path amount Ppseper, the engine 12 is controlled such that the engine 12 is operated at the operation point PNTeng which is deviated from the fuel-economy optimum line and which is dependent on the allowable electrical path amount Ppseper. Thus, in the case in which the differential device 64 is in the gear-ratio fixed state, namely, in which the currently established gear position cannot be switched to another gear position in the differential device 64, the electrical path amount Ppse is limited to the allowable electrical path amount Ppseper that is attainable in the currently established one of the gear ratios γtr of the differential device 64. Thus, the electrical path amount Ppse is appropriately adjusted, so that it is possible to suppress the reduction of the fuel economy which is caused by the deviation of the operation point PNTeng of the engine 12 from the fuel-economy optimum line.

As described, in the present second embodiment, in the event that the differential device 64 cannot execute the shifting action for switching the currently established one of the gear ratios γtr to another one of the gear ratios γtr, the electronic control device 130 is configured to limit the electrical path amount Ppse to the allowable electrical path amount Ppseper that is attainable in the currently established one of the gear ratios γtr of the differential device 64. It is therefore possible to limit the electrical path amount Ppse to an appropriate amount, and accordingly to suppress the reduction of the fuel economy which is caused by the deviation of the operation point PNTeng of the engine 12 from the fuel-economy optimum line. Further, in the present second embodiment, when the differential device 64 can execute the shifting action, substantially the same control operations can be executed as in the above-described first embodiment whereby substantially the same effects can be obtained as in the above-described first embodiment.

Third Embodiment

FIG. 12 is a view schematically showing a construction of a transfer 200 that is other than the transfer 28 of FIG. 4 . Like the transfer 28, the transfer 200 serves as the torque distribution device, and the vehicle driving apparatus 10 is provided with the transfer 200 in place of the transfer 28 in this second embodiment. As shown in FIG. 12 , the transfer 200 includes a transfer case 202 as a non-rotary member (i.e., fixed member), a TF input shaft 204, a differential device 206, the TF clutch CF1, the TF brake BF1, a first output shaft 208, an intermediate shaft 210, the first dog clutch D1, the second dog clutch D2 and a drive gear 212. The TF input shaft 204, differential device 206, TF clutch CF1, TF brake BF1, first output shaft 208, intermediate shaft 210, first dog clutch D1, second dog clutch D2 and drive gear 212 are provided inside the transfer case 202, and are disposed on a common axis in the form of a rotation axis CS1. Each of the differential device 206, TF clutch CF1, TF brake BF1, intermediate shaft 210, first and second dog clutches D1, D2 and drive gear 212 is constructed substantially symmetrically about the rotation axis CL1, so that its lower half (that is located on a lower side of the rotation axis CL1) is not shown in FIG. 12 .

The transfer 200 further includes a second output shaft 214 and a driven gear 216 which are provided inside the transfer case 202 and which are disposed on a common axis in the form of a rotation axis CL2. The driven gear 216 is constructed substantially symmetrically about the rotation axis CL2, so that its upper half (that is located on an upper side of the rotation axis CL2) is not shown in FIG. 12 . The rotation axis CL2 corresponds to an axis of the second output shaft 214, for example.

The transfer 200 further includes the TF rotary electric machine MGF, a pair of connection gears 218 and a chain 220 that are provided inside the transfer case 202. The pair of connection gears 218 consists of a TF rotary-electric-machine connection gear 218 a that is to be rotated integrally with a rotor shaft 222 of the TF rotary electric machine MGF, and a TF counter gear 218 b that constantly meshes with the TF rotary-electric-machine connection gear 218 a. The chain 220 is provided to connect between the drive gear 212 and the driven gear 216.

Like the transfer 28 of FIG. 4 , the transfer 200 further includes a switch actuator (not shown) fixed to the transfer case 202, so as to operate the first and second dog clutches D1, D2. The first sleeve d1 s of the first dog clutch D1 is to be moved by the switch actuator in the direction of the rotation axis CL1. The second sleeve d2 s of the second dog clutch D2 is to be moved by the switch actuator in the direction of the rotation axis CL1.

The TF input shaft 204 is connected to the transmission output shaft 54 in a power transmittable manner. The first output shaft 208 is connected to the rear propeller shaft 32 in a power transmittable manner. The second output shaft 214 is connected to the front propeller shaft 30 in a power transmittable manner. The driven gear 216 is connected to the second output shaft 214, unrotatably relative to the second output shaft 214. The TF counter gear 218 b is connected to the intermediate shaft 210, unrotatably relative to the intermediate shaft 210.

The differential device 206 is constituted by a single-pinion-type planetary gear device, and includes a sun gear S, a carrier CA and a ring gear R. The sun gear S is fixed to the intermediate shaft 210, unrotatably relative to the intermediate shaft 210, so that the TF rotary electric machine MGF is connected to the sun gear S via the pair of connection gears 218, in a power transmittable manner. The carrier CA is connected to the first output shaft 208, unrotatably relative to the first output shaft 208. The ring gear R is selectively connected (engaged) to the transfer case 202 via the TF brake BF1, in a power transmittable manner. The sun gear S and the carrier CA are selectively connected (engaged) to each other via the TF clutch CF1.

The first dog teeth a1 of the first dog clutch D1 is fixed to the TF input shaft 204, unrotatably relative to the TF input shaft 204. The second dog teeth a2 of the first dog clutch D1 is fixed to the first output shaft 208, unrotatably relative to the first output shaft 208. The third dog teeth a3 of the first dog clutch D1 is fixed to the intermediate shaft 210, unrotatably relative to the intermediate shaft 210. It is noted that FIG. 12 shows the first sleeve d1 s of the first dog clutch D1 when the first sleeve d1 s is placed in each of the first state [1] and the second state [2], for convenience of description.

The fourth dog teeth a4 of the second dog clutch D2 is connected to the ring gear R. The fifth dog teeth a5 of the second dog clutch D2 is connected to the first output shaft 208, unrotatably relative to the first output shaft 208. The sixth dog teeth a6 of the second dog clutch D2 is connected to the drive gear 212. It is noted that FIG. 12 shows the second sleeve d2 s of the second dog clutch D2 when the second sleeve d2 s is placed in each of the first state [1], second state [2] and third state [3], for convenience of description.

FIG. 13 is a collinear chart indicating a relationship among rotational speeds of rotary elements of the transfer 200. In FIG. 13 , three vertical lines Y1, Y2, Y3 corresponding to the three rotary elements of the differential device 206 constituting the transfer 200 are an axis representative of a rotational speed of the sun gear S corresponding to the first rotary element RE1, an axis representative of a rotational speed of the carrier CA corresponding to the second rotary element RE2, and an axis representative of a rotational speed of the ring gear R corresponding to the third rotary element RE3, in order from the left side. Further, in FIG. 13 , a vertical line Y0, which is located on a left side of the vertical line Y1, is an axis representative of a rotational speed of the first output shaft 208 corresponding to the input/output rotary element REIO.

As shown in the collinear chart of FIG. 13 , in the transfer 200, the input/output rotary element REIO is selectively connected to the TF input shaft 204 via the first dog clutch D1 that is placed in the first state [1], and is connected to the rear propeller shaft 32. The first power source PU1 including the engine 12 is connected to the TF input shaft 204 via the hybrid transmission 26 in a power transmittable manner. Further, in the differential device 206, the first rotary element RE1 is connected to the TF rotary electric machine MGF in a power transmittable manner, and is selectively connected to the TF input shaft 204 via the first dog clutch D1 that is placed in the second state [2]. The second rotary element RE2 is connected to the first output shaft 208, i.e., the rear propeller shaft 32, and is selectively selected to the second output shaft 214, i.e., the front propeller shaft 30, via the second dog clutch D2 that is placed in the third state [3]. The third rotary element RE3 is selectively connected to the second output shaft 214 via the second dog clutch D2 that is placed in the third state [2], and is selectively connected (engaged) to the transfer case 202 via the TF brake BF1. Moreover, the first and second rotary elements RE1, RE2 are selectively connected (engaged) to each other via the TF clutch CF1. In the collinear chart of FIG. 13 , the relationship among the rotational speeds of the respective first, second and third rotary elements RE1, RE2, RE3 in the differential device 206 is represented by a straight line Lcd. The first output shaft 208 is an output shaft to which the power of the first power source PU1 is to be inputted via the torque converter 48 and from which is the power is to be outputted to the rear wheels 16. The second output shaft 214 is an output shaft from which the power is to be outputted to the front wheels 14.

The differential device 206 can serve as a speed change device configured to establish selectively a high-speed gear position and a low-speed gear position, with the TF clutch CF1 and the TF brake BF1 being provided. The high-speed gear position is established with the TF clutch CF1 being placed in the engaged state. The low-speed gear position is established with the TF brake BF1 being placed in the engaged state.

Further, the differential device 206 serves as a center differential. In this instance, with the first dog clutch D1 being in the first state [1] and with the second dog clutch D2 being in the second state [2] in the transfer 200, the differential device 206 can cause the torque of the first power source PU1 inputted to the second rotary element RE2, to be distributed to the third rotary element RE3, owing a reaction torque of the TF rotary electric machine MGF connected to the first rotary element RE1. Further, the differential device 206 can cause the torque of the first power source PU1 inputted to the second rotary element RE2, to be distributed to the third rotary element RE3, also by limiting the differential effect of the differential device 206 by placing the TF clutch CF1 in a slipping state, in place of applying the reaction torque of the TF rotary electric machine MGF. Thus, the transfer 200 including the differential device 206 is a torque distribution device configured to distribute a part of the torque inputted to the first output shaft 208, to the second output shaft 214, for thereby making it possible to distribute the torque between the front wheels 14 and the rear wheels 16. It is noted that, in the transfer 200, when the second dog clutch D2 is in the third state [3], the differential device 206 is placed in a differential lock state in which the differential device 206 does not function as the center differential.

FIG. 14 is a table indicating a relationship between each mode established in the transfer 200 and controlled states of respective the engagement devices in the transfer 200. In FIG. 14 , “◯” in columns of the TF brake BF1 and the TF clutch CF1 indicates that the TF brake BF1 or TF clutch CF1 is in its engaged state, and blank in the columns of the TF brake BF1 and the TF clutch CF1 indicates that the TF brake BF1 or TF clutch CF1 is in its released state. Further, in FIG. 14 , “◯” in columns of the first and second dog clutches D1, D2 indicates that the first dog clutch D1 or second dog clutch D2 is placed in the corresponding state, and “(◯)” in the column of the first dog clutch D1 indicates that the first dog clutch D1 may be placed in its released state where the first dog clutch D1 can be placed in the released state. The table of FIG. 14 is different from the table of FIG. 6 in that the “EV (FF) HIGH” mode is replaced by “EV (FR) HIGH” mode in number m1 and the “EV (FF) LOW” mode is replaced by “EV (FR) LOW” mode in number m2. The differences of FIG. 14 from FIG. 6 will be described.

Each of the “EV (FR) HIGH” mode of number m1 and the “EV (FF) LOW” mode of number m2 is the BEV driving mode. In the “EV (FR) HIGH” mode and the “EV (FR) LOW” mode, with the second dog clutch D2 being placed in the first state [1], the neutral state (see “N” in FIG. 14 ) is established with any one of the fourth, fifth and sixth dog teeth a4, a5, a6 being not connected to the others of the fourth, fifth and sixth dog teeth a4, a5, a6, so that a power transmission path between the differential device 206 and the front wheels 14 is cut off. In this state in which the second dog clutch D2 being placed in the first state [1], the power of the TF rotary electric machine MGF is transmitted toward the rear wheels 16 in the speed change device 224 in which the high-speed gear position is established with the TF clutch CF1 being in the engaged state or the low-speed gear position is established with the TF brake BF1 being in the engaged state. Thus, in the present embodiment, the BEV running is performed by a rear-wheel drive running. In the BEV driving mode, it is possible to avoid drag of the engine 12, for example, with the automatic transmission 50 being placed in the neutral state when the first dog clutch D1 is in the first state [1]. Where the first dog clutch D1 can be placed in the released state, it is possible to avoid drag of the engine 12 and drag of the automatic transmission 50, with the first dog clutch D1 being placed in the released state, even without the automatic transmission 50 being placed in the neutral state. Further, in the BEV driving mode that is the “EV (FR) HIGH” mode or “EV (FR) LOW” mode, the power of the first power source PU1 can be transmitted to the rear wheels 16, with the automatic transmission 50 being placed in the power transmittable state. For example, in the BEV driving mode that is the “EV (FR) HIGH” mode or “EV (FR) LOW” mode, the HEV running of the vehicle 8 can be performed by transmission of the power of the first power source PU1 to the rear wheels 16 with the first dog clutch D1 being placed in the first state [1].

“H4_TORQUE SPLIT” mode of number m3 is a mode for distributing the torque between the front wheels 14 and the rear wheels 16 at a desired ratio that is dependent on the reaction torque of the TF rotary electric machine MGF, for example, with the torque of the first power source PU1 transmitted from the first output shaft 208 to the differential device 206 being held by the sun gear S to which the reaction torque of the TF rotary electric machine MGF is applied, and with the speed change device 224 being placed in a state corresponding to the high-speed gear position. In the “H4_TORQUE SPLIT” mode established in the transfer 200, the TF rotary electric machine MGF is caused to regenerate the electric power, with which the battery 24 is charged, for example.

“H4_LSD” mode of number m4 is a mode for distributing the torque between the front wheels 14 and the rear wheels 16 at a desired ratio that is dependent on the torque capacity of the TF clutch CF1, by limiting the differential effect of the differential device 206 by placing the TF clutch CF1 in the slipping state, in place of applying the reaction torque of the TF rotary electric machine MGF in the “H4_TORQUE SPLIT” mode.

“H4_Lock” mode of number m5 is a mode for distributing the torque of the first power source PU1 transmitted to the first output shaft 208, between the front wheels 14 and the rear wheels 16, with the differential device 206 being placed in the differential lock state.

“L4_Lock” mode of number m6 is a mode for distributing the torque of the first power source PU1 transmitted to the sun gear S of the differential device 206, between the front wheels 14 and the rear wheels 16, with the differential device 206 being placed in the differential lock state and with the differential device 206 being placed in the low-speed gear position.

Where the transfer 200 is constructed as described above, too, as in the above-described first and second embodiments, during the HEV running of the vehicle 8 with the transfer 200 being placed in the “EV (FR) HIGH” mode or “EV (FR) LOW” mode, the target electrical path amount Ppsetgt, which enables the operation point PNTeng of the engine 12 to become the target operation point PNTtgt, is obtained. Then, the differential device 206 is controlled to establish one of the gear ratios γtr that enables the obtained target electrical path amount Ppsetgt to be attainable, and the electrical path amount Ppse is adjusted to the target electrical path amount Ppsetgt. Further, when at least two of the gear ratios γtr of the differential device 206 enable the obtained target electrical path amount Psetgt to be attainable, one of the at least two of the gear ratios γtr that maximizes the motor efficiency ηmotor of the TF rotary electric machine MGF is selected. Still further, in the event that the differential device 206 cannot execute the shifting action for switching the currently established one of the gear ratios γtr to another one of the gear ratios γtr, the electrical path amount Ppse is limited to the allowable electrical path amount Ppseper that is attainable in the currently established one of the gear ratios γtr of the differential device 206. Thus, in the present third embodiment, too, substantially the same effects can be obtained as in the above-described first and second embodiments.

While the preferred embodiments of this invention have been described in detail by reference to the drawings, it is to be understood that the invention may be otherwise embodied.

For example, in the above-described embodiments, the vehicle driving apparatus 10 is constructed such that the power outputted from the automatic transmission 50 is distributed between the pair of front wheels 14 and the pair of rear wheels 16 via the transfer (28; 200). However, this construction is not essential. For example, the vehicle driving apparatus may include first and second driving devices, wherein the first driving device includes the engine 12, the torque converter 48 and the first rotary electric machine and is configured to transmit the power outputted from the turbine impeller 48 b of the torque converter 48, to one of the pair of front wheels 14 and the pair of rear wheels 16, via the first output shaft, and wherein the second driving device includes the second rotary electric machine and the speed change device configured to change a speed of rotation of the second rotary electric machine and to output the rotation whose speed has been changed and is configured to transmit the power outputted from the second rotary electric machine, to the other of the pair of front wheels 14 and the pair of rear wheels 16, via the speed change device. Further, the operation point of the engine 12 is controllable by adjusting the electrical path amount in the electrical path through which the electric power is to be transferred between the first and second rotary electric machines. Thus, the present invention is applicable also to the vehicle driving apparatus without the transfer configured to distribute the power of the engine 12 to the front and rear wheels, in which the power of the engine 12 is transmitted electrically through the electrical path between the first and second rotary electric machines, to the other of the pair of front wheels 14 and the pair of rear wheels 16. Further, where the vehicle driving apparatus is not provided with the transfer, the power of the second rotary electric machine does not have to be transmitted necessarily to the other of the pair of front wheels 14 and the pair of rear wheels 16, but may be outputted to the first output shaft. That is, the present invention is applicable also to a two-wheel-drive vehicle driving apparatus in which the power of the engine 12 is to be mechanically outputted to the one of the pair of front wheels 14 and the pair of rear wheels 16 via the torque converter 48, and a part of the power of the engine 12 is to be electrically outputted to the same one of the pair of front wheels 14 and the pair of rear wheels 16 through the electrical path between the first and second rotary electric machines.

In the above-described embodiments, values of the motor efficiency ηmotor of the TF rotary electric machine MGF in respective gear ratios γtr of the differential device (64; 206) are obtained and compared with each other, and one of the gear ratios γtr is selected. For example, it is also possible to prepare a two-dimensional map with two variables in the form of the vehicle running speed V and the MGF torque Tmgf of the TF rotary electric machine MGF, which defines a region in which the motor efficiency ηmotor is made higher with the differential device (64; 206) being placed in the low-speed gear position providing the higher gear ratio γtrlow, and another region in which the motor efficiency ηmotor is made higher with the differential device (64; 206) being placed in the high-speed gear position providing the lower gear ratio γtrlow, so that one of the gear ratios γtr is selected with use of the two-dimensional map.

In the above-described embodiments, the differential device (64; 206) may be a transmission configured to establish three or more gear positions, or may be a continuously-variable transmission, too, as long as the differential device (64; 206) is capable of establishing a plurality of gear positions providing the respective different gear ratios γtr.

In the above-described embodiments, during operation of the engine 12, the engine 12 is controlled such that the operation point PNTeng lies on the fuel-economy optimum line. However, the operation point PNTeng does not necessarily have to lie on the fuel-economy optimum line, but the engine 12 may be controlled such that the operation point PNTeng lies in the vicinity of the fuel-economy optimum line.

Further, in the above-described embodiments, the TF clutch CF1 may be also a clutch configured to selectively connect between the first and third rotary elements RE1, RE3 of the differential device (64; 206), or may be also a clutch configured to selectively connect between the second and third rotary elements RE2, RE3 of the differential device (64; 206). That is, the TF clutch CF1 may be configured to selectively connect (engage) between any two of the first, second and third rotary elements RE1, RE2, RE3.

Further, in the above-described embodiments, the vehicle driving apparatus 10 may be modified such that the first output shaft (66; 208) is constituted by an output shaft from which the power, inputted from the first power source PU1 via the torque converter 48, is to be outputted to the front wheels 14, and such that the second output shaft (72; 214) is constituted by an output shaft from which the power is to be outputted to the rear wheels 16.

Further, in the above-described embodiments, the automatic transmission 50 does not necessarily have to be capable of establishing the four forward gear positions, but may be capable of establishing two, three or more than four forward gear positions. Moreover, the automatic transmission 50 may be also a known belt-type continuously variable transmission or a synchronous mesh twin shaft parallel axis-type automatic transmission including a known DCT (Dual Clutch Transmission), for example.

Further, the connection shaft 46 connecting between the engine 12 and the torque converter 48 may be provided with a connecting/disconnecting clutch that is configured to selectively connect and disconnect between the engine 12 and the torque converter 48.

Further, in the above-described embodiments, the fluid transmission device may be constituted by the torque converter 48. However, the fluid transmission device may be constituted by other fluid transmission device such as a fluid coupling device without a function of torque boost effect, in place of the torque converter 48.

It is to be understood that the embodiments described above are given for illustrative purpose only, and that the present invention may be embodied with various modifications and improvements which may occur to those skilled in the art.

NOMENCLATURE OF ELEMENTS

-   10: vehicle driving apparatus -   12: engine -   14: front wheels (the other of the pair of front wheels and the pair     of rear wheels) -   16: rear wheels (one of the pair of front wheels and the pair of     rear wheels) -   28; 200: transfer (torque distribution device) -   44; 202: transfer case (fixed member) -   48: torque converter (fluid transmission device) -   48 a: pump impeller (input-side rotary element) -   48 b: turbine impeller (output-side rotary element) -   64; 206: differential device (speed change device) -   66; 208: first output shaft -   72; 214: second output shaft -   130; 150: electronic control device (control device) -   MGM: TM rotary electric machine (first rotary electric machine) -   MGF: TF rotary electric machine (second rotary electric machine) -   CF1: TF clutch (first engagement device) -   BF1: TF brake (second engagement device) -   RE1: first rotary element -   RE2: second rotary element -   RE3: third rotary element -   L1: first power transmission path -   L2: second power transmission path 

What is claimed is:
 1. A driving apparatus for a vehicle that includes a pair of front wheels and a pair of rear wheels, the driving apparatus comprising: (a) an engine; (b) a fluid transmission device including (b-1) an input-side rotary element configured to receive a power from the engine and (b-2) an output-side rotary element configured to output the power received by the input-side rotary element; (c) a first rotary electric machine connected to the input-side rotary element; (d) a first output shaft which is configured to receive the power outputted by the output-side rotary element and transmitted through a first power transmission path and which is configured to output the power to one of the pair of front wheels and the pair of rear wheels; (e) a second rotary electric machine; and (f) a control device configured to control an operation point of the engine by adjusting an electrical path amount that is an amount of an electric power in an electrical path through which the electric power is to be transferred between the first and second rotary electric machines, wherein the second rotary electric machine is configured to output the power to the first output shaft or the other of the pair of front wheels and the pair of rear wheels, through a second power transmission path that is other than the first power transmission path, wherein the second power transmission path is provided with a speed change device that is configured to change a speed of rotation of the second rotary electric machine in accordance with a currently established one of gear ratios that is established in the speed change device and to output the rotation whose speed has been changed, wherein the control device is configured to obtain a target electrical path amount as a target amount of the electrical path amount that enables the operation point of the engine to become a target operation point, and to control the speed change device based on the obtained target electrical path amount so as to establish one of the gear ratios that enables the obtained target electrical path amount to be attainable; and wherein the control device is configured to adjust the electrical path amount to the obtained target electrical path amount, and to control the operation point of the engine.
 2. The driving apparatus according to claim 1, wherein, when at least two of the gear ratios enable the obtained target electrical path amount to be attainable, the control device is configured to cause the speed change device to establish one of the at least two of the gear ratios that maximizes an efficiency of the second rotary electric machine.
 3. The driving apparatus according to claim 1, wherein, in an event that the speed change device cannot execute a shifting action for switching a currently established one of the gear ratios to another one of the gear ratios, the control device is configured to limit the electrical path amount depending on the currently established one of the gear ratios.
 4. The driving apparatus according to claim 1, comprising a second output shaft configured to output the power to the other of the pair of front wheels and the pair of rear wheels, wherein the speed change device includes: a differential device including a first rotary element connected to the second rotary electric machine, a second rotary element connected to one of the first and second output shafts and a third rotary element connected to the other of the first and second output shafts, the differential device constituting a torque distribution device that is configured to distribute a part of a torque inputted to the first output shaft, to the second output shaft; a first engagement device configured to connect and disconnect between two of the first, second and third rotary elements; and a second engagement device configured to connect and disconnect between the third rotary element and a non-rotary member. 